Transactional Model

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The transactional database model is part of a class of nonrelational data models which includes the hierarchical, network, and inverted list models. The term transactional refers to the data access method used to navigate up, down, and sideways through data records. This method provides direct control and allows a developer to optimize data access based on knowledge of the underlying structure of the data. Btrieve is an example of a transactional database engine.

A transactional database allows you to find a specific record within a file and navigate to an adjacent record, the first record, the last record, or yet another specific record. This type of database access is quite fast. This is because the section of the file that contains the requested record (typically referred to as a page) is stored in the cache, or memory. Adjacent records, which are probably related to the current record and could be called next, are also placed in memory because they are a part of the same page as the current record. The following figure illustrates an example page.

 
Figure 3-1 Transactional Files and Records

The powerful MicroKernel engine is the basis of all Pervasive Software database products; it manages all of the low-level database functions for both the relational and transactional interfaces. In either case, the engine allows you to access records in their physical order, their logical order, or both. Physical order refers to the physical location of the data in the file. Logical order, on the other hand, is a conceptual construct that organizes the records according to some specified system based on part(s) of the data. Examples of logical ordering include alphabetical ascending or descending order.