X.500 Standard status
X.509 Related activities
How to be involved
Tutorial section 1
Tutorial section 2
X.509 at work
For directory information to be usable and accessible, it has to be organised in a pre-defined way. The rule for how directory information is organised is called the directory schema. The directory schema is made up of several elements:
All the above types of schema elements, and few more, determine the characteristics of an entry and its relation to other entries.
For a Directory System Agent (DSA), that is, a directory server, to contain a particular entry it is necessary for the DSA to have implemented all the schema elements that govern the characteristics of that entry.
For a Directory User Agent (DUA), that is, a directory client, to access this entry and utilise the stored information it must also have a pretty good understanding of all the schema elements. If a user through his DUA accesses different Directory domains, he would expect the same type of information, like an e-mail address, to be controlled by the same schema element independent of location, otherwise the DUA may not be able to utilise the information.
If all organizations, like Internet, private organizations, national groups, etc. each independently makes own directory schema definitions, which is somewhat the case today, it will not be possible to make a truly integrated European Directory. Even though it may be possible to physically interconnect different domains, they will not be able to utilise each other's information.