h2. AttributeType

The *AttributeType* is one of the most important schema element. It describes what can be stored into an *[DIRAPI:Entry]*, its syntax, and the various rules that are to be followed when searching for an associated value.

*AttributeType* are immutable objects, created from the schema, and never changed. One can add a new *AttributeType*, or delete itfrom the schema, but once it's added to the schema, it can't be modified.

Usually, we just use them. 

h3. Description

!error.png! : mandatory
!check.png! : optional
!warning.png! : warning


An *AttributeType* contains the following informations :

|| Value || Description || optional ||
| OID | An unique *[DIRAPI:Oid]* for the *AttributeType* | !error.png! |
| NAME | some names, the fist one being considered as the _short name_. | !check.png! |
| DESCR | A textual description describing the *AttributeType* role. | !check.png! |
| OBSOLETE | A flag indicating if the *AttributeType* is deprecated | !check.png! |
| SUP | The *AttributeType* it inherit from | !warning.png! If SYNTAX is null, can't be null |
| EQUALITY | The EQUALITY *[MatchingRule (e)]* | !check.png! if null, and if SUP is not null, takes its SUP's value |
| ORDERING | The ORDERING *[MatchingRule (e)]* | !check.png! if null, and if SUP is not null, takes its SUP's value |
| SUBSTR | The SUBSTR *[MatchingRule (e)]* | !check.png! if null, and if SUP is not null, takes its SUP's value |
| SYNTAX | The Syntax to follow | !warning.png! If SUP is null, can't be null |
| SINGLE-VALUE| Tells that the *AttributeType* does not allow more than one value | !check.png! |
| COLLECTIVE | Define a collective attribute. The *AttributeType* USAGE must be _userApplications_ | !check.png! |
| NO-USER-MODIFICATION | Tells that the values can't be modified by the user. The *AttributeType* USAGE must be operational | !check.png! |
| USAGE | The kind of *AttributeType* : one of \{ _userApplications_, _directoryOperation_, _directoryOperation_, _directoryOperation_\}| !check.png! |
| extensions | Server specific parameters | !check.png! |

An *AttributeType* has some default elements : it's not OBSOLETE, has no SUP, is not SINGLE-VALUE, is not COLLECTIVE, can be modified by the user, and has an _userApplications_ USAGE.