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A Powerful Database Subsystem

A fast and extremely flexible database subsystem makes Visual Prolog a more suitable choice for database applications than many 4GLs. The database system supports a collection of distinct ordered chains of Prolog terms, where database terms can be any abstraction supported by the language itself, from simple records to trees or graphs. The database system can directly access individual terms, or it can backtrack through chains of terms to generate or match particular values. The terms can be stored in any one of three locations: in a file, in memory or in EMS-type expanded memory under DOS. The database also supports B+ trees, which provide fast data retrieval and the ability to change term ordering efficiently.

If you are using the database in a LAN application, you can take advantage of Visual Prolog's support for file sharing in the external database system. Multi-user database access is provided using a mechanism that efficiently serializes file access inside of transactions. This means that a database can be open by several users or processes simultaneously.