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Programming Interfaces
Data Management : Database Access : Sequences : Choosing between sequences and control tables
Choosing between sequences and control tables
Sequences are objects, like fields, that you can create and maintain in any OpenEdge database. Unlike fields, sequences reside in a separate database block independent of application tables. The following figure shows the basic relationship between database fields and sequences.
Figure 7. Database fields and sequences comparison
Each sequence has a name and a value, similar to a field. But unlike a field, a sequence also has different schema attributes that determine how the sequence value can change. These include:
*Whether the sequence increments or decrements and by what interval
*Whether the sequence cycles or terminates
*The upper and lower boundaries for sequence values
ABL provides a dedicated set of functions and statements to access and increment sequences strictly according to the defined attributes.
* Using sequences or control tables
* Performance versus capabilities
* Transaction independence
* Storage limits