Every GDB in ObjectLand has a name which meets the usual requirements to the file name.
From the point of view of operating system GDB is represented by nine or ten files located in one and the same folder. Their names are based on GDB name.
Why are there so many files for one GDB? No, there are not many at all. Even when working with usual DBMS the number of files for one database is often measured in many tens.
Figure nine and file names are connected with the data storage structure accepted in ObjectLand. Without going into details we can say that all the data in one GDB is divided into definition database, table database and map database. Every database is stored in three files: definitions file, index file and data file.
The rules according to which file names from GDB name are formed are presented in table 3-1.
Definition database | Table database | Map database | |
Definitions files | <GDB name>.GDB | <GDB name>0.TBL | <GDB name>1.MAP |
Data files | <GDB name>.DAT | <GDB name>0.DAT | <GDB name>1.DAT |
Index files | <GDB name>.ASS | <GDB name>0.ASS | <GDB name>1.ASS |
Table 3-1 GDB file names
In table 3-2 all file names for the GDB named City are given
Definition database | Table database | Map database | |
Definitions files | City.GDB | City0.TBL | City1.MAP |
Data files | City.DAT | City0.DAT | City1.DAT |
Index files | City.ASS | City0.ASS | City1.ASS |
Table 3-2 GDB “City” file names
Definitions file contains data dictionary describing the data structure in the data files (DAT) and index files (ASS) connected with it.
Index file contains indexes necessary for quick search in the data file.
Data file, as you may guess, contains the data itself. In the definition database it is GDB style library, and also descriptions of structures of all the maps, themes, tables and queries kept in GDB. In table database – all records of all GDB tables. In map database – all features of all the maps and also information about the links between features and table records.
Apart from nine main GDB files, a part of data can be temporarily stored in the change file which has CHG extension. Using the change file is described in chapter 5 “GDB opening”.
Data in GDB files is organized as pages of the fixed size. The user can select the page size for files of different types. Since the maximal number of pages is limited, the page size influences the maximal GDB file size.
During ObjectLand work auxiliary files may be created, such as report, settings, rollback files and so on. They are not part of GDB structure.
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