content/api/user-guide/6.4-attribute-type.mdtext

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# 6.4 - AttributeType

The _AttributeType_ is one of the most important schema elements. It describes what can be stored into an _Entry_, its syntax, and the various rules that are to be followed whenever 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. 

## Description

An _AttributeType_ contains the following informations:

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

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.

You can check some of those elements using the following methods:

* isAncestorOf( AttrbuteType ) : tells if the current _AttributeType_ is the ancestor of another one
* isCollective() : tells if the current _AttributeType_ is a collective attribute
* isDescendantOf( AttributeType ) : tells if the current _AttributeType_ inherits from another one
* isOperational() : tells if the current _AttributeType_ is an Operational Attribute
* isSingleValued() : tells if the current _AttributeType_ does not allow more than one value
* isUser() : tells if the current _AttributeType_ is a User Application _AttributeType_
* isUserModifiable() : tells if the _Attributes_ usng this _AttributeType_ can be modified on the server