WWW: Beyond the Basics

15. Searching and Databases on the Web

15.5. Retrieval

The retrieval module provides the original resources to the user. There are mainly two models for retrieval: direct retrieval and client-server retrieval.

15.5.1 Direct retrieval

If the original resource is stored in the index (database), the retrieval is trivial. In this case, the user can retrieve the original document directly. In the searching and retrieval process of the traditional database, the database service and interface are closed protocols, and reside on a single mainframe computer. The search engine accepts query from the user with query language, and searches the database, and then retrieves resources or documents from the database, returns them directly to the user.

15.5.2 Client-server retrieval

Usually what the user got (the result set) is an index of the original resources or documents, or a list of URLs. The index may resides on a separated server from the original resources. In this case, the user has to do retrieval through internet as the usual client-server service does, which is the client-server retrieval model. In the client-server retrieval process, the client (the user) send retrieval request to the server, the sever locates the resource or document and returns it to the client, and then the client displays it appropriately. The Web browser and the Web server are working this way. So are most search systems on the World Wide Web. The server and the clients communicate with certain standard interface or protocols. For examples, TCP/IP and UDP are popular protocols used on Internet; HTTP protocol is a standard protocol used by the Web (or Mosiac, Netscape). Z39.50 search and retrieval standard is a communication protocol officially recognized by the American National Standards Organization (ANSI) National Information Standards Organization (NISO) as an international standard for communication. WAIS (Wide Area Information Server), the most popular Web indexing and searching method currently used on the Web, is based on the Z39.50 standard.

[PREV] [NEXT] [UP] [HOME] [VT CS]

Copyright © 1996 Aixiang (I Song) Yao, All Rights Reserved

Aixiang (I Song) Yao<ayao@csgrad.cs.vt.edu>
Last modified: November 21, 1996