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The IMesh Toolkit
[ Work In Hand > Technology Review > Standards and Protocols ]
Lightweight Directory Access Protocol (LDAP) |
Overall Purpose |
| Lightweight Directory Access Protocol is a lightweight standardised directory access protocol. It runs on top of TCP/IP. The first widely available version was LDAP version 2, defined in RFCs 1777 and 1778. LDAP developed out of the X500 directory service, which was seen to be large, complex and difficult to implement. |
Brief Overview of Functionality |
Four models give guidance on the
organisation of data in the directory. The LDAP information model
defines the kind of data that can be put into the directory; the
LDAP naming model defines how directory data is organised and
referred to in the directory; the LDAP functional model defines
how directory information is accessed and updated; the security
model defines how the information can be protected from
unauthorised access. The basic unit of the directory is an entry.
Entries consist of attributes; each attribute has a type and one
or more values. An entry has a globally-unique Distinguished
Name, used to refer to the entry unambiguously. Directory entries
are arranged in a hierarchical tree-like structure. LDAP is a
client/server protocol. The LDAP protocol is message-based.
Clients issue requests to servers (simultaneous multiple requests
can be made) and servers return entries to the client. LDAP has
nine basic protocol operations, divided into three categories:
|
Deployment |
| APIs
The original LDAP distribution from the University of Michigan (U-M LDAP) included a C programming library and several sample client programs built on this library. The LDAP C API for LDAP version 2 is documented in RFC 1823, and the University of Michigan Software Development Kit is available at: http://www.umich.edu/~dirsvcs/ldap/. Other C SDKs are:
A Java API has also been developed by Netscape http://www.mozilla.org (source code). The API specification is at http://www.ietf.org. PerlLDAP is available from http://www.mozilla.org. Another Perl LDAP SDK is Net::LDAP which is available from http://www.perl.com/CPAN. Accessing multiple directory systems JavaSoft and Microsoft have proprietary SDKs that define an interface for accessing multiple directory systems. Microsoft's ADSI (Active Directory Services Interface) is available for VisualBasic, C and C++ http://www.microsoft.com. The Javasoft product JNDI (Java Naming and Directory Interface) is available from http://www.javasoft.com. A number of different directory systems can be accessed from a Java application or applet. Projects using or investigating LDAP The Isaac Network This is a project of the Internet Scout Project team, who are partners in the IMesh toolkit project. The Isaac Network proposes to link geographically distributed collections of metadata into a virtual collection searchable as a unified whole. It uses the Dublin Core as its standard metadata description format. It aims to provide a single user interface to the user for sending a single query, which will reach all relevant subject gateways and return relevant results back to the user. The Isaac Network is unique in achieving this goal in that it uses the shared indexing capabilities of the Common Indexing Protocol (CIP) and the query-routing capabilities of LDAP. The Isaac system claims to be the first to use an LDAP directory for metadata records about resources, and to combine LDAP with CIP in a distributed index-sharing and query-routing architecture. Isaac consists of three main software components: the metadata repository, the search service and the index service. Within the system, LDAP is operated as follows: The metadata database of the metadata repository is made accessible via LDAP. Referral (query-routing) information is kept by each repository. Using the search service any user (or LDAP application) may have their queries routed to appropriate repositories and processed in parallel. This is possible because of the referral capabilities of the LDAP protocol. A 1999 paper proposed using LDAP as the basis of a cataloguer's interface to the system, since LDAP supports add, delete and modify operations. TF-LSD (Task Force - LDAP Services Deployment) A task force has been established within the technical programme of TERENA [http://www.terena.nl/] the trans-European Research and Education Networking Association, to investigate the usability of LDAPv3 as a base for a wide range of Internet services. TF - LSD will operate for two years from 1st October 2000. The major objectives of the TF-LSD [http://www.terena.nl/task-forces/] are:
|
Related Standards |
| LDAP runs over a TCP/IP connection. There is a variety of options for the backend database giving flexibility in the choice of storage for data. |
Relevance to IMesh context |
| Use of LDAP for searching metadata has been demonstrated in the Isaac Network. LDAP is a protocol that could be used for making resource descriptions (metadata) available in a directory-based model. |
References |
| Understanding and Deploying LDAP Directory
Services, Howes, T.A., Smith, M.C. and Good, G.S., Macmillan
(1999). Sample chapter available at: http://www.computerbooksonline.com/chapters/ldapchap.htm The Isaac Network: LDAP and Distributed Metadata for Resource Discovery http://computer.org/proceedings/meta/1999/papers/46/clukas.html OpenLDAP version 2 administrator's guide. http://www.openldap.org/doc/admin/intro.html#What is LDAP |
Other Standards and Protocols |
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