Probably the first operations you perform with a DBMS are the creation and definition of objects that hold your data, objects that define relationships between the data, and objects that allow you to restrict access to the data. With Microsoft Jet, you can create and modify the following types of objects.
All Microsoft Jet objects are contained in a single file known as a database file. This file contains both object definitions and data.
Tables can contain data in a native Microsoft Jet format, or they can represent links to data stored in a variety of other data formats such as Microsoft Exchange, Microsoft Excel, FoxPro, or ODBC data sources such as Microsoft SQL Server.
A variety of field data types are available, including Text, Number, Currency, and Memo. Tables can contain up to 255 fields. Microsoft Jet supports both variable-length and fixed-length fields. For example, text fields store only the amount of text in the field; extra space isn’t wasted in the database file to pad out the field to its maximum size.
Microsoft Jet allows both primary and secondary indexes that can be based on one or more fields. You can create indexes by using both DAO and SQL.
In a Microsoft Jet database, relationships define how data in multiple tables is related. With Microsoft Jet, you can use Relation objects to define relationships between fields and enforce referential integrity with cascading updates and deletes.
You can create and save a variety of query types by using Microsoft Jet, including queries for data retrieval and data manipulation.
To implement security, Microsoft Jet uses a form of workgroup security that defines users and the groups to which they belong. User and Group objects represent specific users and groups who are authorized to use Microsoft Jet.
Applications that use Microsoft Jet can store their own objects in the database. These objects are maintained through a Containers collection. For example, Microsoft Access uses Container objects to store its forms, reports, macros, and modules.
See Also For more information on data definition, see Chapter 3, “Data Definition and Integrity.”