## Directory Class Definitions

The X.500 standards define a number of attribute types and classes. These definitions allow the creation and maintenance of directory entries for a number of common objects so that the representation of all such objects is the same throughout the directory. The basic directory contents package contains OM classes and OM attributes that model the X.500 attribute types and classes.

The X.500 object classes and attributes are defined in the following documents published by CCITT. These are the objects and the associated attributes that will be the targets of directory service operations in your application programs:

· The Directory: Selected Attributes Types (Recommendation X.520)

· The Directory: Selected Object Classes (Recommendation X.521)

The table below describes the OM classes, OM attributes, and their object identifiers that model the X.500 objects and attributes. (See Basic Directory Contents Package for more tables with the same type of information.)

Representation of Values for Selected Attribute Types

Attribute Type | OM Value Syntax | Value Length | Multi-valued | Matching Rules
DS_A_ALIASED_ OBJECT_NAME | Object(DS_C_NAME) | - | no | E
DS_A_BUSINES_ CATEGORY | String(OM_S_ TELETEX_STRING) | 1-128 | yes | E, S
DS_A_COMMON_NAME | String(OM_S_ TELETEX_STRING) | 1-64 | yes | E, S
DS_A_COUNTRY_NAME | String(OM_S_ PRINTABLE_STRING) As permitted by ISO 3166. | 2 | no | E
DS_A_DESCRIPTION | String(OM_S_ TELETEX_STRING) | 1-1024 | yes | E, S

The tables in Basic Directory Contents Package contain similar categories of information as do similar tables for the attributes defined in the directory service package. These information categories include the following:

· OM Value Syntax

· Value Length

· Multivalued

· Matching Rules

The OM Value Syntax column describes the structure of the values of an OM attribute. The Value Length column gives the range of lengths permitted for the string types. The Multivalued column indicates whether the attribute can have multiple values.

The CCITT standards define matching rules that are used for determining whether two values are equal, for ordering two values, or for identifying one value as a substring of another in directory service operations. These are indicated in the Matching Rules column.

The GDS administrator maintains the directory service and determines the structure of the DIT as defined by the GDS schema. The GDS standard (or default) schema is based on the recommendations in the CCITT documents mentioned previously.

Recall that the structure rule table (SRT) of the GDS schema defines the structure of the DIT, the object class table (OCT) defines class inheritance properties, and the attribute table (AT) defines the mandatory and optional attributes for each class. You will find it useful to familiarize yourself with the existing schema when developing an application program that will access the directory. This is because the public objects that your programs will create (by using OM classes and OM attributes) are modeled after objects and attributes in the directory.

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