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Summary
The Data Dictionary is a tool that you use to create, view, and modify the properties of a database and database objects: tables, fields, indexes, and sequences. Database properties include those that define database objects and those that establish application defaults. Collectively, database properties are referred to as schema.
Databases have two names:
The Data Dictionary allows you to connect databases. When a database is connected, any Progress tool or application can access the data or schema of the database.
Table objects are defined with a unique name. The definitions of constituent fields and indexes make up the bulk of a table definition.
Field objects are defined with a unique name and by specifying a data type. Data types determine what kind of data a field can store:
Index objects are defined by specifying a name and the component fields. Other index properties define how the index works:
Sequences are objects that generate automatic incremental sequences. Using sequence properties, you can define three types of sequences:
- Nonterminating sequences start at an initial value and increment continually in one direction with no limit.
- Terminating sequences start at an initial value and increment in one direction toward a limit. Upon reaching the limit, a terminating sequence ceases to generate new values.
- A cycling sequence starts at an initial value and increments in one direction toward a limit. Upon reaching the limit, the sequence starts over at the initial value.
Tables and fields have a validation property, which allow you to check criteria before allowing record deletions in a table or new values in a field. The validation property is made up of:
Databases have special events for which you can write triggers:
- A CREATE event occurs when a new record is created.
- A DELETE event occurs when a record is deleted.
- A FIND event occurs when any search successfully finds a record.
- A WRITE event occurs when Progress writes a record back to the database.
- An ASSIGN event occurs when Progress writes new data to an individual field.
The database trigger property allows you to add default behaviors to a database, eliminating the need to code the behaviors in your procedures.
Field formats are symbols that tell Progress how you want to display data by default. Formats do not affect the actual data, just the display of the data.
Connected database
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