Databases-Chapter 2 Flashcards
Data models
Data model
Relatively simple representation ,usually graphical, of more complex real-world data structures
Importance of data models
It represents data structures and their entities, characteristics, relationships, constraints and transformations
Saves costs, reduces development time, decreases errors
Improves understanding of the business and
Improves communication between role players on the project
Entity
A real world object distinguishable from others
they have attributes and relationships
Business rules
Are brief, precise and unambiguous descriptions of policies, procedures or principles within a specific organization(help to create and enforce actions within that org’s environment)
Business rules must be:
-Rendered in writing
-Apply to any organization that stores and uses data to generate information
-Must be kept up to date to reflect any change in the org’s operational environment
-Sometimes are external to the organization
-Easy to understand and widely disseminated to ensure that every person in the org shares a common interpretation of the rules
-Describes characteristics of the data as viewed by the company
Sources of business rules
-Company managers
-Policy makers
-Department managers
-Written documentation(procedures, standards, operations manuals)
-Direct interviews with end users
SQL involves
User interface
A set of tables stored in the database
SQL engine
Data abstraction
Is the reduction of a certain portion of data for a simple presentation of content
The process of removing features from something to reduce the set of necessary features
American national standards institute(ANSI)
Standards Planning and requirements committee(SPARC)
Defined a framework for data modeling based on degrees of data abstraction(1970s)
The external model
Hardware and software independent
End users’ view of the data environment
Use business rules
Highest level of abstraction
The external model advantages
-Easy to identify specific data required to support each business unit’s operations
-Facilitates designer’s job by providing feedback about the model’s adequacy
-Creation of external models helps to ensure security constraints in the database design
-Simplifies app program development
The conceptual model
-Represents global view of the entire database
-Provides a relatively easily understood macro level view of data environment
-Independent of both software and hardware
The internal model
-Representation of the database as seen by the DBMS
-Maps the conceptual model to the DBMS
-Internal schema depicts a specific representation of an internal model
Physical model
-Operates at the lowest level of abstraction, describing the way data are saved on storage media such as disks or tapes
-Software/hardware dependent
-Requires that database designers have a detailed knowledge of the hardware and software used to implement database design
The process of identifying and documenting business rules is essential to database design for several reasons:
-They help standardize the company’s view of data
-They can be a communications tool between users and designers
-They allow the designer to understand the nature, role and scope of the data
-They allow the designer to develop appropriate relationship participation rules and constraints and to create an accurate model
-They allow the designer to understand business processes
End-user interface
The interface allows the end user to interact with the data(by auto-generating SQL code)
A collection of tables stored in the database
All data are perceived to be stored in tables, easier to understand
SQL engine
Executes all queries or data requests, SQL engine is part of the DBMS software
Unified Modelling language
Language that describes a set of diagrams and symbols that can be used to model a system graphically
Relational data model Advantages
Data/structural independent
-Structural independence is promoted by the use of independent tables. Change in a tables structure do not affect data access/app programs
-Tabular view substantially improves conceptual simplicity
-Ad hoc query capability is based on SQL
-Powerful RDBMS isolates the end user from physical-level details and improves implementation and management simplicity
Relational data model disadvantages
-The RDBMS requires substantial hardware and system software overhead
-Conceptual simplicity gives relatively untrained people tools to use a good system poorly, and if unchecked it may produce the same data anomalies found in the file systems
-It may promote islands of info problems as individuals and departments can easily develop their applications
