An attribute consists of an
attribute identifier and a
set of
attribute values.
The
attribute identifier, also called
attribute name,
is a string that identifies an attribute.
An
attribute value is the content of the attribute and its type
is not restricted to that of string.
You use an attribute name when you want to
specify a particular attribute for either retrieval,
searches, or modification. Names are also returned by operations
that return attributes (such as when you perform reads or searches
in the directory).
When using attribute names,
you need to be aware of certain directory server features
so that you won't be surprised by the result.
These features are described in the next subsections.
Attribute Type
In directories such as the LDAP, the attribute's name identifies the
attribute's type and is often called the
attribute type
name. For example, the attribute name
"cn" is also called the
attribute type name. An attribute's type definition specifies the
syntax that the attribute's value is to have, whether it can have
multiple values, and equality and ordering rules to use when
performing comparison and ordering operations on the attribute's values.
Attribute Subclassing
Some directory implementations support
attribute subclassing,
in which the server allows attribute types to be defined in
terms of other attribute types. For example,
a
"name" attribute might be the superclass of all name-related
attributes:
"commonName" might be a subclass of
"name".
For directory implementations that support this,
asking for the
"name" attribute might return the
"commonName" attribute.
When accessing directories that support attribute subclassing,
you have to be aware that the server might return
attributes that have names different from those that
you requested.
To minimize the chance of this, use the most derived subclass.
Attribute Name Synonyms
Some directory implementations support synonyms for attribute
names. For example,
"cn" might be a synonym for
"commonName".
Thus a request for the
"cn" attribute might
return the
"commonName" attribute.
When accessing directories that support synonyms for attribute names,
you must be aware that the server might return
attributes that have names different from those you requested.
To help prevent this from happening, use the canonical
attribute name instead of one of its synonyms.
The canonical attribute name is the name used in the attribute's definition;
a synonym is the name that refers to the canonical attribute name in its
definition.
Language Preferences
An extension to the LDAP v3
(
RFC 2596)
allows you to specify a language code along with an attribute name.
This resembles attribute subclassing in that
one attribute name can represent several different attributes.
An example is a
"description" attribute that has two
language variations:
description: software
description;lang-en: software products
description;lang-de: Softwareprodukte
A request for the
"description" attribute would return all three attributes.
When accessing directories that support this feature,
you must be aware that the server might return
attributes that have names different from those
that you requested.
