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Directories – More Than Just Information Storage Directories are rapidly becoming the cornerstone to delivering flexibility for advanced services, both as means of storing location information, user configuration and resource privileges and as a means of storing servicespecific information allowing for rapid provisioning of customers and rapid modification of services. One of the key issues that directories will resolve for the next-generation networks is the dynamic nature of the future services and the desire to reach services based on useful textbased naming | Next Generation Network Services Neill Wilkinson Copyright 2002 John Wiley Sons Ltd ISBNs 0-471-48667-1 Hardback 0-470-84603-8 Electronic 9 Directories - More Than Just Information Storage Introduction Directories are rapidly becoming the cornerstone to delivering flexibility for advanced services both as means of storing location information user configuration and resource privileges and as a means of storing servicespecific information allowing for rapid provisioning of customers and rapid modification of services. One of the key issues that directories will resolve for the next-generation networks is the dynamic nature of the future services and the desire to reach services based on useful textbased naming. In the previous chapter on representing information we explored a number of exciting uses of Extensible Markup Language XML to allow applications to discover and use services none of this discovery process would work without directories. I start this chapter with a brief look at the domain name system DNS possibly the best-known directory system since most of us use it every day. I continue the chapter by looking at and Lightweight Directory Access Protocol LDAP . is the International Telecommunications Union ITU standard for directory technologies and whilst complex is arguably the most influential of all the directory technologies. We then take a look at the concept of meta-directories directory systems that link other directories together. 116 DIRECTORIES - MORE THAN JUST INFORMATION STORAGE Domain Name System DNS The DNS was created to overcome the scaling problems associated with the distribution of a text file based database that listed all the hostnames and their Internet protocol IP addresses. The main part of the DNS is the definition of a hierarchical naming scheme based on a domain model and a distributed database directory . Two application components are used to interrogate the database a resolver for the client .