Physical Model

A DP4 database is stored in these files:

• The Data (.DAT) file contains all the records stored on the database. From release 4.622 the Data file may be stored in a compressed format.
• The Data Compression Information (.DCI) file, introduced in release 4.622, contains vital information needed to decode data stored in compressed data files.
• The Index (.IND) file contains all the indexes for all the records on the database.
• The Pointer (.PTR) file, introduced in release 4.622, used with databases using a new more space efficient index structure, stores a cross reference between record numbers and the location of the corresponding record in the data file.
• The transaction log (.LOG) or temporary transaction log (.RLL) is used to safely store new transactions in the database until such time as the database stored on disk is fully updated.
• The rollback (.RLB) file is used to safely recover the database after a system failure.

In addition there are various other files associated with the DP4 system. All these files are described in more detail in the following topics:

• Data and Index Files
• Roll-back and Transaction Logs
• Other Files
• DP4 Runtime Files
• Base Dictionary
• Location of Database Files