LDAP vs relational database (Part 2)
By treydrake on Feb 22, 2007
Universal drivers: No vendor specific database drivers are needed as LDAP specifies a standard wire protocol. That is, any vendor’s LDAP client should be interoperable with any other vendor’s directory server. Therefore, the onerous task of obtaining and managing vendor database drivers is no longer necessary.
LDAP controls: Controls provide a mechanism for both the client and the server to send additional information with a LDAP request. A very useful LDAP control is persistent search (not all servers support the control, but it is a common feature). This control notifies the search requester of a change in the search results. For example, if an application centrally stores configuration information in a directory it needs to be notified if the configuration is changed. This is easily accomplished by running a persistent search on the config data - if a change (add, modify, delete, move) occurs the server will asynchronously notify the client. Checkout controls supported by OpenDS.
URL based searches: Depending on the capabilities of your LDAP client, a standardized URL may be used to execute a search; e.g., ldap://localhost/dc=example,dc=com???(uid=treydrake) returns the entry associated with “treydrake”. With a bit of practice, fine grained entry/attribute retrieval and search criteria is easily expressed on the "web command line". Not quite ReST, but convenient nonetheless.
LDAP schema constructs: I've noted that LDAP schema consists of objectclasses and attributes. A point worth mentioning is that objectclasses are much more flexible than flat RDBMS tables. Specifically, there are 3 types of objectclasses: structural, abstract, and auxiliary. Structural types are concrete classes that represent an LDAP entry. Abstract classes are simply structural parents; i.e., they define attributes for inheritance by more specialized, structural classes. Finally, auxiliary types are supplemental classes that may be associated with structural or abstract classes. To make these concepts concrete consider the typical person example, "inetorgperson" (the LDAP standard defines numerous standard objectclass types, one of which is "inetorgperson"). This type is derived as follows: top -> person -> organizationalPerson -> inetorgPerson. Where top is the parent of all LDAP classes and inetorgperson defines new person attributes and inherits all superior objectclass attributes. Objectclass inheritance is a heck of a lot cleaner than defining numerous tables and linking them together with foreign keys!
Globally unique schema: An interesting aspect of LDAP schema is the identification of objectclasses and attributes as globally unique objects known as OIDs. That is, every attribute and objectclass has both a name and a unique ID. This makes sharing schema objects throughout the enterprise much more precise and traceable as an OID is associated with an authority (a company, standard, etc). For example, I may create an objectclass named "blog" with the OID 184.108.40.206.4.1.26922.1.1. OIDs are also hierarchal; breaking apart the OID, "220.127.116.11.4.1" identifies the object is owned by a private enterprise, "26922" identifies the specific enterprise and the trailing suffix "1.1" is completely defined by the enterprise. An enterprise, having defined a new globally unique object, may then publish a detailed description of the new objectclass for reference by consumers. Clearly, identifying schema elements with collision proof ids versus names is a distinct advantage. Need your own OID namespace? Get one here.