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Date: Tue, 05 Nov 1996 21:47:55 GMTServer: NCSA/1.5Content-type: text/htmlLast-modified: Thu, 19 Jan 1995 17:35:08 GMTContent-length: 7401<HTML><HEAD><TITLE>URLs and the CS Web Server</TITLE></HEAD><BODY><P> <H2>URLs and the CS Web Server</H2><P> <H3>Introduction</H3><P> One of the design features of the Web is ``hypertext.'' Hypertext is theidea of creating a link from part of one document to another part of a document (either the same document, or a different one). The concept is really no different than a cross-reference, but the referenced documentis available to the user in an instant.<P> In a hypertext system some standard method of specifying links must becreated. The designers of the Web decided that for their needs, the mostappropriate way to specify the start of a link was to mark a section of adocument with special tags (see the <!WA0><!WA0><!WA0><!WA0><A HREF="http://www.cs.wisc.edu/docs/htmltutorial.html#links">HTML tutorial</A>). Specifying the ``destination'' of the link was more complicated, because each part of each document on the internet had tohave a unique ``name''. To solve the problem, they created the <EM>UniformResource Identifier</EM> or <EM>URI</EM> specification. The syntax ofURIs was designed to be:<DL> <DT> <EM>Extensible</EM>. <DD> That is, new kinds of links can be added if necessary. <DT> <EM>Complete</EM>. <DD> It is possible to specify any naming scheme within a URI. <DT> <EM>Printable</EM> <DD> Any URI uses only 7-bit ASCII characters, and is designed to be easily readable.</DL><P> The URI specification was in turn used to write specifications for the naming of documents or services available through existing internet protocols. These initial specifications were named<EM>Uniform Resource Locators</EM> or <EM>URLs</EM>. In this documentwe discuss some of the commonly used URL specifications.<P> <H3>The CS http server and relative URLs</H3><P> When people talk about putting documents on the Web, they are usuallyreferring to putting their document in the namespace of a <EM>HypertextTransfer Protocol</EM> or <EM>HTTP</EM> server. HTTP was designed tosatisfy the curious needs of the Web, namely the quick, anonymous retrieval of documents.<P> The http server provides each user with their ownWeb namespace, starting in the directory <TT>~/public/html</TT>. Theserver has the permissions of any other user, so the files in this directory must be readable by any user. We will describe what the fullURL of this namespace later in this document. <P> URLs are similar to pathnames in a file-system, and just as with pathnamesit is possible to construct relative URLs. In a Unix shell, pathnames namefiles relative to a ``working directory.'' URLs name documents relative tothe URL of the document a link is being made <EM>from</EM>. Roughly speaking,if when you make a link from document <EM>a</EM> to document <EM>b</EM> andyou leave out parts of the URL for <EM>b</EM>, those parts will be copied fromthe URL that was used to retrieve <EM>a</EM>. <P> For example, if I have a document called <TT>home.html</TT>, and I wantto make a link from it to another document called <TT>todo.html</TT>, I cansimply use the relative URL ``<TT>todo.html</TT>''. If I have a third document in a subdirectory <TT>data</TT> called <TT>results.html</TT>, I can use the relative URL ``<TT>data/results.html</TT>'' to link toit from <TT>home.html</TT> (URLs generally use the ``/'' character to separate directory names, just like Unix). To link from <TT>data/results.html</TT> to <TT>home.html</TT> you could use the relative URL ``<TT>../home.html</TT>''.<P> The name the http server uses for each user's web names pace is``<TT>/~<EM>username</EM>/</TT>''. Remember that this points to the subdirectory <TT>~<EM>username</EM>/public/html/</TT> and not to <TT>~<EM>username</EM>/</TT>. If you wanted to link to my home pagefrom a document in your directory, you could use the relative URL``<TT>/~keeper/keeper.html</TT>''. <P> <H3>Full URLs</H3><P> To link to a file or service that is not on the CS http server, youneed to know its full URL. To link to documents on other http servers, a full URL looks like the following:<BLOCKQUOTE><PRE>http://<EM>fqdn</EM>/<EM>pathname</EM></PRE></BLOCKQUOTE><P> Where <EM>fqdn</EM> is the ``fully-qualified domain name'' (as in<TT>www.cs.wisc.edu</TT>). (Sometimes a server will be running on a portother than the standard one, in which case you follow the <EM>fqdn</EM> with a colon and the port number, as in <TT>monty.cs.wisc.edu:1080</TT>.)The full URL for the home page of the CS department is:<BLOCKQUOTE><PRE>http://www.cs.wisc.edu/</PRE></BLOCKQUOTE><P> The home page is located at the root of the tree. The full URL for my home page is:<BLOCKQUOTE><PRE>http://www.cs.wisc.edu/~keeper/keeper.html</PRE></BLOCKQUOTE><P> Another useful URL type is <TT>ftp</TT>, which allows you to link to fileson anonymous FTP servers. The format is exactly the same as <TT>http</TT>URLs, except <TT>http</TT> becomes <TT>ftp</TT>. The URL for the <TT>condor</TT> directory on the CS FTP server is:<BLOCKQUOTE><PRE>ftp://ftp.cs.wisc.edu/condor/</PRE></BLOCKQUOTE><P> <H2>Access Control, Tricks, and Details</H2><P> <H3>Linking to parts of documents</H3><P> To create a link to a specific part of a document, that document mustbe written in HTML, and contain a named anchor (see the <!WA1><!WA1><!WA1><!WA1><A HREF="http://www.cs.wisc.edu/docs/htmltutorial.html#links">tutorial</A>). The URL would simply be theURL of the file followed by a hash mark (``#'') and the name of the anchor.If the anchor is in the same document the URL is just ``<TT>#<EM>anchorname</EM></TT>''. <P> <H3>Access Control</H3><P> The http server provides an access control system similar to the<!WA2><!WA2><!WA2><!WA2><A HREF="http://www.cs.wisc.edu/csl/faq/software/afs.html#acl">access control lists</A> in AFS, but because all the files are already on AFS you should use it rather than the server to <!WA3><!WA3><!WA3><!WA3><A HREF="http://www.cs.wisc.edu/csl/faq/software/afs.html#set_acl">protect your files</A>.<P> <H3>Mapping documents to directories</H3><P> Normally when the server gets a request for the URL of a directory itreturns a list of files. However, if a file named <TT>index.html</TT> exists in the directory it is sent instead. The CS home page is stored inthe file <TT>index.html</TT> in the root directory. Many people like tomake a link from <TT>index.html</TT> to their home page (as in <TT> ln -s <EM>username</EM>.html index.html</TT>) so that when the URL<BLOCKQUOTE><PRE>http://www.cs.wisc.edu/~<EM>username</EM>/</PRE></BLOCKQUOTE><P> is requested their home page is returned.<P> <H3>Searching directly with URLs</H3><P> Each Web browser has a method for sending a search string to a remote server, and many Web services rely on this search string. Luckily, themethod used for sending the string is to translate and append it to the URL of the service preceded by a question mark. The translation changesspaces to plus signs (``+'') and encodes other seldom-used special charactersin hexadecimal. The finger script on our server uses this feature. To make a link that fingers a user from a document on our server, you can use the relative URL:<BLOCKQUOTE><PRE>/cgi-bin/finger?<EM>username</EM></PRE></BLOCKQUOTE><P> <H2>Related Documents</H2>If you want to continue learning about URLs a list of other references is <!WA4><!WA4><!WA4><!WA4><A HREF="http://www.cs.wisc.edu/docs/otherdocs.html#url">here</A>. You might also want to continuereading <!WA5><!WA5><!WA5><!WA5><A HREF="http://www.cs.wisc.edu/docs/">our documents</A>.</BODY></HTML>⌨️ 快捷键说明
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