Views Chapter 12

What Are Views? A virtual table that comprises the fields of one or more tables in the database It is a virtual table since it does not store or contain data Only its structure is saved; the data is re- created each time it is accessed

Value of Views They can be used to work with data from two or more tables They reflect the most up-to-date information They can be fitted to the specific needs of an individual or group They can be used to help enforce data integrity They can be used for security or confidentiality purposes

Anatomy of a View Views can be based on a single table, multiple tables, other views or a combination of tables and values Can use the fields from the structures they comprise Structures that compose the view are called base tables or base views

Data Views Used to examine and manipulate data from base tables Certain fields from the base tables are used to create the view’s structure Data in a single-table data view can be modified at any time (except when there are rules that specify otherwise)

Data Views (cont.) Data views based on two or more tables can be created as well as long as relationship exist Data redundancy is allowed since it is not a real table that stores data A view does not contain a primary key

Aggregate Views Purpose is to display information that is the result of aggregating a particular set of data in a specific manner Includes one or more calculated fields that incorporate the functions that aggregate the data and one or more data fields to group the aggregate data

Aggregate Views (cont.) Data cannot be modified in an aggregate view –Calculated fields are noneditable –Data fields are used for grouping purposes only Best used as the basis of a report or as a means of providing various types of statistical information

Validation Views Similar to validation tables in that they are used to implement data integrity Must be explicitly defined since it will store data Constructed with fields from base tables and draws data from those tables Usually built from a single table and comprise only two or three fields

Determining and Establishing Views Views can be a substantial asset to the database Views are used as a tool to support particular aspects of the implementation or application program

Working with Users and Management Identify the types of views required by the organization Suggestions to identify requirements: –Review notes with the group –Review data-entry report, and presentation samples gathered during the early stages of the design process –Examine the tables and subjects they represent –Analyze the table relationships –Study the business rules

Establishing Views Using calculated fields where appropriate Imposing Criteria to Filter the Data Using a View Specifications Sheet to Record the View –Name –Type –Base Tables –Calculated Field Expressions –Filters

Reviewing the Documentation for Each View Make certain that the view is properly constructed Make certain that the calculated fields created are suitable for the View Make certain that the filters will retrieve the required records Make certain that a view diagram and View Specifications Sheet exists for each view