Grouping Directory EntriesChapter 4 Designing the Directory Tree 77About Class of ServiceA class of service (CoS) allows you to share attributes between entries in a way thatis invisible to applications. With CoS, some attribute values may not be stored withthe entry itself. Instead, they are generated by class of service logic as the entry issent to the client application.For example, your directory contains thousands of entries that all share thecommon attribute facsimileTelephoneNumber. Traditionally, to change the faxnumber, you would need to update each entry individually, a large job foradministrators that runs the risk of not updating all entries. With CoS, you cangenerate the attribute dynamically. The facsimileTelephoneNumber attribute isstored in one place, and each entry points to that place to give a value to their faxnumber attribute. For the application, these attributes appear just like all otherattributes despite not actually being stored on the entries themselves.Each CoS is comprised of the following entries in your directory:• CoS Definition Entry — The CoS definition entry identifies the type of CoS youare using. It is stored as an LDAP subentry below the branch it affects.• Template Entry — The template entry contains a list of the shared attributevalues. Changes to the template entry attribute values are automaticallyapplied to all the entries sharing the attribute.The CoS definition entry and the template entry interact to provide attribute valuesto their target entries, the entries within their scope. The value they providedepends upon the following:• The entry’s DN (different portions of the directory tree might contain differentCoS).• A service class attribute value stored with the entry.The absence of a service class attribute can imply a specific default CoS.• The attribute value stored in the CoS template entry.Each CoS template entry supplies the attribute value for a particular CoS.• The object class of the entry.CoS attribute values are generated only when an entry contains an object classallowing the attribute when schema checking is turned on; otherwise, allattribute values are generated.• The attribute stored in some particular entry in the directory tree.
