Midterm Review Flashcards
(40 cards)
What is a database system?
- Computerized record-keeping system
- A collection of programs to create and maintain database
- Supports operations (ex. insert, retrieve, remove, or change data in database)
- Components (ex. data, hardware, software, users)
What are the two types of databases?
- Single-user database: supports one user at a time
- Multiuser database: supports multiple users at the same time
What is a database?
- Collection of persistent data that is used by the application systems of some given enterprise.
- Collection of true propositions (ex. “Supplier S1 is located in London”)
What are the three elements that form a database?
- Entities
- Relationships
- Properties
What are the three types of data?
- Static (e.g. part#, SIN)
- Dynamic (e.g. quantity, balance)
- Quasi-static (e.g. salary)
What are the 8 reasons to use a database?
- Shared data
- Reduced redundancy
- Reduced inconsistent data
- Transaction support
- Support for data integrity
- Security enforcement
- Support for standards
- Conflicting requirements can be met
What is shared data?
Data can be used to operate existing applications as well as develop new ones.
What is data redundancy?
Keeping data in two or more places within a database or data storage system.
How can data redundancy lead to data inconsistency?
When database updates are not propagated to all redundant data.
What is data integrity?
The overall accuracy, completeness, and consistency of data.
For example:
- We shouldn’t have an employee working in a non-existent department.
- We shouldn’t have the number of hours entered as 400 instead of 40.
How can database security be enforced?
- Restricting unauthorized data
- Different checks (security constraints) can be established for each type of access (retrieve, insert, delete, etc.)
What are the five functions of DBMSs?
- Data dictionary management
- Security management
- Multiuser access control
- Backup and recovery management
- Data integrity management
What are some disadvantages of database systems?
- Increased costs
- Management complexity
- Vendor dependence
- Frequency upgrade/replacement cycles
What is the difference between a database instance and database schema?
Schema: description of the database
Instance: database itself
What is database schema?
- Describes the database
- Specified during the database design phase (not expected to change frequently)
- Most data models have a notation for graphical representation of schema.
What is a database instance?
- Refers to the data in the database at a particular moment in time.
- Can correspond to a particular schema.
- Every time we insert, delete, or update the value of a data item, we change one instance of database to another.
What are the 3 levels in ANSI/SPARC architecture?
- Internal Level
- Conceptual Level
- External Level
What is the internal level in ANSI/SPARC architecture?
Shows how data are stored inside the system. It is the closest level to the physical storage.
This level talks about database implementation and describes such things as file organization and access paths.
What is the conceptual level in ANSI/SPARC architecture?
Deals with the modeling of the whole database. The conceptual schema of database is defined in this level.
What is the external level in ANSI/SPARC architecture?
This level models a user-oriented description of part of the database. External schemas define individual users’ views at this level.
What is database mapping?
The process of matching fields from one database to another. The key to providing data independence.
What are the two types of data independence?
- Logical data independence
- Physical data independence
What is logical data independence?
Ability to modify conceptual schema without changing external views or application programs. Provided by external/conceptual mapping.
What is physical data independence?
Ability to modify internal or physical schema without changing conceptual or view level schema, or application programs.
