Normalisation Chapter Flashcards
(333 cards)
1
Q
What does normalisation ensure?
A
No data redundancy
Thus removing the possibility of update anomalies
Normalisation helps to identify a suitable set of relations to represent data in the database
2
Q
Stronger definition of 3NF was subsequently defined
A
Boyce-Codd Normal Form
3
Q
Database schema
A
Consists of a group of relations
4
Q
Relation
A
Consist of a set of attributes
5
Q
When the Data requirements of an organisation are identified, how are these attributes grouped into suitable relations?
A
The common sense of the database designer.
By mapping ER diagrams onto relations.
6
Q
Functional dependencies
A
a functional dependency is a constraint between two sets of attributes in a relation from a database
Let R be
NewStudent(stuId, lastName, major, credits, status, socSecNo)
FDs in R include
{stuId}→{lastName}, but not the reverse
{stuId} →{lastName, major, credits, status, socSecNo, stuId}
{socSecNo} →{stuId, lastName, major, credits, status, socSecNo}
{credits}→{status}, but not {status}→{credits}
7
Q
Normalisation
A
Is the process of testing the correctness of a logical data model
8
Q
What attributes are classed
A
Key attributes
Non-key attributes
9
Q
Normalisation is a formal method
It identifies relations based on:
A
Primary key and the functional dependencies between their attributes
10
Q
Update anomalies
A
To minimise data redundancy thus reducing file storage space
11
Q
What are the three categories of update anomalies
A
Insertion anomalies
Delete anomalies
Modification anomalies
12
Q
Insert a branch that currently has no members of staff into the staffBranch relation
A
To do this you must enter NULL in the attributes of staff but Staff_No is a primary key, primary key may not be NULL
13
Q
If we remove a staff member from the StaffBranch relation we also remove information about the branch at which they work.
If the staff member happened to be the last member at this branch
What will happen?
A
We lose all details of that branch from the database
14
Q
Change the telephone number for branch B3 in the StaffBranch relation
A
We must update the rows of all staff located at branch B3
If some of the rows are not updated, this results in inconsistent data
15
Q
A -> B
What does this tells us?
A
A is said to be the determinant
B is said to be the dependent
16
Q
Un-normalisation form
A
Contains one or more repeating groups
Attributes values are non-atomic
17
Q
A relation is in 1NF if
A
It contains no repeating groups
All non key attributes are functionally dependent on the primary key
18
Q
A relation is in 2NF if
A
It is in 1NF
All non key attributes are fully functionally dependent on the primary key
19
Q
B is fully functionally dependent on A if
A
B is functionally dependent on A and not any subset of A
20
Q
B is partially dependent on A if
A
some attribute can be removed from A and the dependency still holds
21
Q
A relation is in 3NF if
A
It is in 2NF
Non Key attributes are not transitively dependent on the primary key
22
Q
If A,B and C are attributes of a relation and
A->B and B->C
A
Then C is transitively dependent on A via B
23
Q
Key attributes/non-key attributes example
A
Key attributes: A key attribute is the unique characteristic of the entity. For ex. Name and hire date are attributes of the entity Employee
Non-Key Attributes: Non-key attributes are attributes that are not part of a key. Consider attributes for first name, last name, birth date;
24
Q
Full functional dependency example
A
Definition: A full functional dependency occurs when you already meet the requirements for a functional dependency and the set of attributes on the left side of the functional dependency statement cannot be reduced any farther
Examples: For example, “{SSN, age} -> name” is a functional dependency, but it is not a full functional dependency because you can remove age from the left side of the statement without impacting the dependency relationship.
25
Transitive dependency example
a transitive dependency is a functional dependency which holds by virtue of transitivity
A → B
It is not the case that B → A
B → C
26
Insertion anomaly
user is unable to insert a new record of data when it should be possible to do so because not all other information is available
27
Deletion anomaly
Deletion anomaly – when a record is deleted, other information that is tied to it is also deleted
28
Update anomaly
Update anomaly –a record is updated, but other appearances of the same items are not updated
29
anomaly
An anomaly is an inconsistent, incomplete, or contradictory state of the database
30
database
A database is a collection of records stored on some type of media. Storage in the past has included punch cards, paper tape, magnetic tapes and disks.
31
Advantages and Limitations for database
Advantages
Reduced data redundancy
Reduced updating errors and increased consistency
Greater data integrity and independence from applications programs
Improved data access to users through use of host and query languages
Improved data security
Reduced data entry, storage, and retrieval costs
However, the following can be viewed as some of the limitations of a database:
Disadvantages
Database systems are complex, difficult, and time-consuming to design
Substantial hardware and software start-up costs
Damage to database affects virtually all applications programs
Extensive conversion costs in moving form a file-based system to a database system
Initial training required for all programmers and users
32
Stages in Creating a Database
Data analysis,Physical implementation
33
An entity
An entity is an instance of a given entity type
34
An entity occurrence example
An entity occurrence is an instance of an entity
| eg: Billy Jones (ie: SN12345, Billy, Jones, 18/08/1950)
35
attribute
An attribute is an item of information which is stored about an entity
36
Entity Integrity
Entity integrity is a basic constraint of database relational model (abbreviated RM) that refers to the morphology of the primary key.
37
Referential Integrity
Referential integrity is a relational database concept, which states that table relationships must always be consistent. In other words, any foreign key field must agree with the primary key that is referenced by the foreign key.
38
cardinality
uniqueness of data values contained in a particular column (attribute) of a database table
39
participation
A relationship instance is two entities of one or two types associated by virtue of a defined relationship between them
40
Structural independence
Structural independence exists when it is possible to make changes in the file structure without affecting the application programs ability to access the data
41
relational model
The relational model (RM) for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by Edgar F. Codd.[1][2] In the relational model of a database, all data is represented in terms of tuples, grouped into relations.
The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.
42
Phantom Reads
Phantom Reads
Phantom reads occur when an insert or delete action is performed against a row that belongs to a range of rows being read by a transaction.
For example, an editor makes changes to a document submitted by a writer, but when the changes are incorporated into the master copy of the document by the production department, they find that new unedited material has been added to the document by the author.
43
Locking Protocol
A locking protocol is a set of rules followed by all transactions while
requesting and releasing locks. Locking protocols restrict the set of
possible schedules.
44
Deadlock , avoided , prevented,
In a database, a deadlock is a situation in which two or more transactions are waiting for one another to give up locks. For example, Transaction A might hold a lock on some rows in the Accounts table and needs to update some rows in the Orders table to finish.
avoided : resources currently available;
resources currently allocated to each process;
resources that will be required and released by these processes in the future.
prevented: To prevent any deadlock situation in the system, the DBMS aggressively inspects all the operations, where transactions are about to execute
45
Entity
Is an instance of a given entity type
46
Entity type
Is a category of a thing or object for example students, horses
47
Relationships
Is some association between entities
48
transaction and what properties
A transaction symbolizes a unit of work performed within a database management system (or similar system) against a database
properties: ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably.
49
Lost updates examples
Lost updates occur when two or more transactions select the same row and then update the row based on the value originally selected. Each transaction is unaware of other transactions. The last update overwrites updates made by the other transactions, which results in lost data
For example, two editors make an electronic copy of the same document
50
Uncommitted Dependency
```
Uncommitted Dependency (Dirty Read)
Uncommitted dependency occurs when a second transaction selects a row that is being updated by another transaction. The second transaction is reading data that has not been committed yet and may be changed by the transaction updating the row.
For example, an editor is making changes to an electronic document.
```
51
Inconsistent Analysis
```
Inconsistent Analysis (Nonrepeatable Read)
Inconsistent analysis occurs when a second transaction accesses the same row several times and reads different data each time. Inconsistent analysis is similar to uncommitted dependency in that another transaction is changing the data that a second transaction is reading. However, in inconsistent analysis, the data read by the second transaction was committed by the transaction that made the change. Also, inconsistent analysis involves multiple reads (two or more) of the same row and each time the information is changed by another transaction; thus, the term nonrepeatable read.
For example, an editor reads the same document twice, but between each reading, the writer rewrites the document.
```
52
Attributes
An entity is characterised by a number of attributes
53
Cardinality
Cardinality concerns the number of instances of an entity involved in a relationship
54
Weak entity type
Is an entity type whose existence depends on the existence of another two entities
55
Participation give example
A relationship instance is two entities of one or types associated by virtue of a defined relationship between them
Eg. Catherine Horgan cares people's
56
Mandatory membership example
Membership of an entity type in a relationship is mandatory if each entity of a type must participate in an instance under that relationship
Eg. A lecturer teaches at least one module
57
Optional membership example
Membership of an entity type in a relationship is optional if entities of a type can exist without participating in an instance under that relationship
Ex. A lecturer may teach some module.
Ex. A lecturer may not teach any modules
58
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
59
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
60
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
61
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
62
Database management system
A database management system (DBMS) is system software for creating and managing databases
63
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
64
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
65
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
66
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
67
Database management system
A database management system (DBMS) is system software for creating and managing databases
68
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
69
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
70
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
71
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
72
Database management system
A database management system (DBMS) is system software for creating and managing databases
73
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
74
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
75
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
76
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
77
Database management system
A database management system (DBMS) is system software for creating and managing databases
78
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
79
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
80
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
81
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
82
Database management system
A database management system (DBMS) is system software for creating and managing databases
83
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
84
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
85
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
86
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
87
Database management system
A database management system (DBMS) is system software for creating and managing databases
88
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
89
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
90
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
91
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
92
Database management system
A database management system (DBMS) is system software for creating and managing databases
93
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
94
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
95
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
96
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
97
Database management system
A database management system (DBMS) is system software for creating and managing databases
98
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
99
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
100
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
101
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
102
Database management system
A database management system (DBMS) is system software for creating and managing databases
103
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
104
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
105
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
106
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
107
Database management system
A database management system (DBMS) is system software for creating and managing databases
108
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
109
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
110
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
111
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
112
Database management system
A database management system (DBMS) is system software for creating and managing databases
113
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
114
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
115
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
116
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
117
Database management system
A database management system (DBMS) is system software for creating and managing databases
118
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
119
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
120
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
121
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
122
Database management system
A database management system (DBMS) is system software for creating and managing databases
123
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
124
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
125
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
126
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
127
Database management system
A database management system (DBMS) is system software for creating and managing databases
128
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
129
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
130
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
131
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
132
Database management system
A database management system (DBMS) is system software for creating and managing databases
133
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
134
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
135
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
136
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
137
Database management system
A database management system (DBMS) is system software for creating and managing databases
138
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
139
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
140
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
141
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
142
Database management system
A database management system (DBMS) is system software for creating and managing databases
143
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
144
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
145
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
146
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
147
Database management system
A database management system (DBMS) is system software for creating and managing databases
148
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
149
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
150
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
151
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
152
Database management system
A database management system (DBMS) is system software for creating and managing databases
153
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
154
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
155
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
156
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
157
Database management system
A database management system (DBMS) is system software for creating and managing databases
158
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
159
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
160
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
161
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
162
Database management system
A database management system (DBMS) is system software for creating and managing databases
163
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
164
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
165
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
166
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
167
Database management system
A database management system (DBMS) is system software for creating and managing databases
168
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
169
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
170
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
171
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
172
Database management system
A database management system (DBMS) is system software for creating and managing databases
173
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
174
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
175
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
176
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
177
Database management system
A database management system (DBMS) is system software for creating and managing databases
178
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
179
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
180
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
181
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
182
Database management system
A database management system (DBMS) is system software for creating and managing databases
183
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
184
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
185
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
186
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
187
Database management system
A database management system (DBMS) is system software for creating and managing databases
188
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
189
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
190
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
191
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
192
Database management system
A database management system (DBMS) is system software for creating and managing databases
193
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
194
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
195
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
196
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
197
Database management system
A database management system (DBMS) is system software for creating and managing databases
198
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
199
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
200
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
201
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
202
Database management system
A database management system (DBMS) is system software for creating and managing databases
203
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
204
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
205
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
206
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
207
Database management system
A database management system (DBMS) is system software for creating and managing databases
208
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
209
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
210
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
211
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
212
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
213
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
214
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
215
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
216
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
217
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
218
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
219
Sql
Mobile-friendly - SQL (Structured Query Language) is a standard interactive and programming language for getting information from and updating a database
220
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
221
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
222
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
223
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
224
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
225
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
226
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
227
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
228
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
229
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
230
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
231
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
232
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
233
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
234
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
235
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
236
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
237
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
By the 2PL protocol locks are applied and removed in two phases:
Expanding phase: locks are acquired and no locks are released.
Shrinking phase: locks are released and no locks are acquired.
Two types of locks are utilized by the basic protocol: Shared and Exclusive locks. Refinements of the basic protocol may utilize more lock types. Using locks that block processes, 2PL may be subject to deadlocks that result from the mutual blocking of two or more transactions.
238
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
239
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
240
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
241
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
242
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
243
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
244
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
245
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
246
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
247
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
248
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
249
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
250
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
251
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
252
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
253
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
254
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
255
2PL locking protocol
two-phase locking (2PL) is a concurrency control method that guarantees serializability
256
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
257
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
258
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
259
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
260
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
261
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
262
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
263
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
264
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
265
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
266
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
267
Why normalise a relational scheme
Helps to identify a set of relatives data in the database
268
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
269
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
270
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
271
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
272
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
273
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
274
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
275
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
276
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
277
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
278
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
279
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
280
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
281
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
282
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
283
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
284
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
285
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
286
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
287
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
288
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
289
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
290
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
291
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
292
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
293
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
294
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
295
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
296
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
297
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
298
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
299
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
300
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
301
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
302
Involuted relationships
A relationship in which the two entity types of the relationship are from the same entity type.
303
Parallel relationships
Two or more relationships which exists between the same two entity types
304
Super/ sub entity types
A collection of entities of the same type to which a narrower
305
Aggregate functions
An aggregate is a collection of items that are gathered together to form a total quantity
306
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
307
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
308
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
309
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
310
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
311
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
312
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
313
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
314
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
315
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
316
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
317
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
318
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
319
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
320
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
321
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
322
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
323
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
324
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
325
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
326
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
327
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
328
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
329
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
330
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
331
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
332
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
333
Data independence
Data independence is the type of data transparency that matters for a centralized DBMS
