Physical Database

An ODABA database consists of one or more files. Each database may consist of a number of main bases, which may consist of a number of data areas. The definition of main bases and data areas if part of the physical database definition. Typically, the database has only one main base (main base 0) with one data area (data area 0). In this case, no explicit physical database definition is required.

This chapter also provides a very technical description for the physical database structure. Data in an ODABA database is organizes in database entries. Each database entry provides some meta information besides the actual data. Data in a database entry may contain object instance data or data for collection indexes. Database entries are addressed by local object identifiers (LOID), which are internal unique numbers for each database entry.

An ODABA database provides two ways of accessing data: directly by LOID (as far as it is known to the application) or via content hierarchies starting by locating an object space and an extent, an instance, a property and than an instance again and so on. Always from an instance one may access a property and from a (collection) property the next instance.