X.500 calls the complete directory database, the Directory Information Base (DIB) and considers it as a single, logical, global directory database eventhough it can be distributed over the network and spread over many DSAs.
The DIB stores information on directory objects such as people, machines, processes etc. Each object has attributes attached to them.
For example, people objects may have attributes such as their names, telephone numbers home and business addresses.
It is also possible that we shall want to address a person by his organisational role, rather than by thier actual name and such objects can be defined and stored in the DIB.
In general there are no restrictions as to the kind of objects and attributes which can be defined in the directory. The X.521 Recommendation defines a number of selected sets of attributes and object classes which are considered useful over a range of applications of the X.500 global directory. Click Here for example.
Some of the attribute types and attribute syntaxes are internationally standardised.
For example, the IDD dialling code is standardised in a format where a country code is followed by an area code, which is followed by a local number. However, in the main, the syntax and semantics of the data which can be stored is nowhere near international standardisation.
In order that we can locate the correct entry within the DIB, the information held within the DIB must be unambiguously defined.
One way of achieving this is to employ a hierarchical tree structure. X.500 defines a logical tree structure for the DIB, called the Directory Information Tree.