A/WWW Enterprises15 July 1996 Implementing Queries with HTTP A. Warnock A/WWW Enterprises

A/WWW Enterprises15 July 1996 Why Use Open Protocols? n Anyone can write servers n Anyone can write clients n Leverages off of existing development n Uses formalized standards n In short:Interoperability

A/WWW Enterprises15 July 1996 What Protocols Are Available? n ftp n telnet n gopher (really telnet) n WAIS (Z ) n http + CGI n Z39.50 v2, v3

A/WWW Enterprises15 July 1996 http Capabilities n http does only a few things get files (w/ MIME type) put parameters (from forms) execute scripts (CGI) n http defines only syntax, not content n Queries depend on content

A/WWW Enterprises15 July 1996 CGI Scripting n CGI runs scripts on server accepts parameters from client parameter input via command line or stdin pipes output to stdout n Sample CGI Input Stream cgi-bin/ ? The parameter list is unspecified - it can be anything the form implementor desires

A/WWW Enterprises15 July 1996 Search Requirements n Search = Bookkeeping + Query n Bookkeeping consists of: User ID inf. What database to query? What elements to return? What format is requested? How many records to return?

A/WWW Enterprises15 July 1996 What Goes Into A Query? n A query is constructed by specifying: Search Term(s) Field Names Words, phrases, etc. Word stems, wildcards Stems, substrings, area relations n None of these is prescribed in http!

A/WWW Enterprises15 July 1996 http Query Summary n http can transmit arbitrary queries, but contains nothing to help in interpreting them n We must make up and agree upon a query syntax from scratch n This is called a Search Profile

A/WWW Enterprises15 July 1996 Example Scenario n User completes an HTML form and submits it n Server receives a POST request - a bunch of information: Where the message came from How long the message is The message text

A/WWW Enterprises15 July 1996 Sample Query n Step 1: /cgi-bin/query?db=Inventory &user=warnock&nrecs=all&element=B &format=HTML&platform=Landsat7TM &rect=42N+112.5W+center+512km+NS +512km+EW&operator=spatialIntersect &resolution=Maximum n Must also include all state information

A/WWW Enterprises15 July 1996 Critique n What’s so hard about this? Is the query case sensitive? What if the user is French? Russian? Chinese? Do I specify “platform” or “Platform” or “Source” or “source”? Is the order of parameters important? How do I specify other resolutions? Can you generalize this to the query in Step 9? What’s your confidence that it would be correct?

A/WWW Enterprises15 July 1996 Summary n http can be used to transmit queries and responses, but there’s nothing in the protocol itself to make the process unambiguous n We have to do all the work outside the protocol - that is, we have to write a profile!