Overview

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<p>This document describes the key aspects of DLXS User Interface technology.
 
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It is intended as a fairly high level overview. It applies to DLXS Image, Text,
 
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and FindAid Classes, but not Bib Class which lags behind in support for XML
 
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and XSL. </p>
 
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==Introduction==
 
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<p>The DLXS Classes are CGI based web applications written using the Perl
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===Text Class Behaviors Overview===
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programming language. The CGIs operate
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between the web server and the data, and are also known as <em>middleware</em>.
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The middleware is designed to keep data handling tasks separate from user interface
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tasks as much as possible. The combination of Perl programming code, XML, and
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XSLT help to achieve this. Each page served is created by generating
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an XML data document and transforming it using XSLT to HTML for display in
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the browser. </p>
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<p>It is beyond the scope of this documentation to teach the fundamentals of
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Perl, XML, XSLT and HTML. You may find you can comprehend most of
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this documentation even if you are not very familiar with some of the technologies.
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We will start with a high level view, increasing the complexity as we go. </p>
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<p>The diagram below illustrates how a CGI takes an XML template,
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populates it with data, and transforms it to HTML using an XSL stylesheet.</p>
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[[Image:dlxsxmlxslhtml.png]]
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==Breakdown of Components==
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===XML Templates===
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<p>An XML template exists for every page in the DLXS system. An XML
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template is an XML file that contains
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placeholders, called <strong>Processing Instructions</strong>. It is the starting
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point for what will be an XML document full of dynamically generated data. </p>
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<p>Templates vary depending on the purpose of the page. A search form page has
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different requirements that a search results page, and the templates reflect
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this. </p>
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Take a look at this complete [http://www.dlxs.org/training/workshop200707/ui/search_template.xml XML template (Not all browsers can display XML. Try Firefox.). It is for a search form page in Text Class.
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===XML===
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<p>The CGI produces an XML document as a result of replacing a templates <strong>Processing
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Instructions</strong>. The XML contains all of the data to be displayed in
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the browser, however, the it lacks the formatting instructions needed by
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the browser to display an attractive and functional user interface. </p>
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<p>Take a look at this <a href="search.xml" target="_blank">XML </a> document.
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It is the template above after having the PIs replaced by the CGI.</p>
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<p>XML documents used in the user interface are totally different than the XML
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documents that hold content such as the full text of a book or an electronic
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Finding Aid, though portions of content will replace PIs in the XML for search
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results page. If you want to know more about preparing data as XML, see <a href="http://dlxs.org/docs/13/data/index.html">Data
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Issues for DLXS</a>.</p>
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===Processing Instructions===
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<p><strong>Processing Instructions</strong> or<strong> PIs</strong> are replaced
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by the CGI with
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dynamically generated data such as search results, and information used to
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construct menus, forms and links in the user interface. Every Processing Instruction
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is paired with a handler in the CGI for replacing the PI with data or other
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information. </p>
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<PI_IDENTIFIER_NAME [modifiername=&quot;value&quot;]*?>
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<p>Above you can see the generic form of a Processing Instruction. PIs can optionally
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have modifiers, though most do not. Modifiers pass additional information to
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the CGI, affecting the replacement. </p>
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<p>Processing Instructions are usually wrapped by XML tags for structure and
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context. Some PIs get replaced by small amounts of data, such as the word &quot;true&quot;
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or &quot;false&quot;, while others are replaced by large amounts of data, sometimes containing
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additional XML tags.</p>
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<p>The diagram below shows a snippet of the XML template. </p>
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[[Image:xmltemplatesnip.png]]
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<p>Next you see the snippet of the XML after Processing Instructions
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have been replacedby the CGI. </p>
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[[Image:xmlsnip.png]]
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===XSL===
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<p>XSL is the programming language used to transform the XML to HTML. An XSL
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program is more commonly called an XSL Stylesheet. Each XML file specifies
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the XSL Stylesheet to be used for transformation. It is common in DLXS for
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one stylesheet to incorporate several other stylesheets stored in separate
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files (for the convenience of sharing code). More on this later.</p>
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<p>Take a look at this <a href="searchforms.xsl" target="_blank">XSL Stylesheet</a>.
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It is one of the stylesheets used to transform XML to HTML for the search form
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page in Text Class. You might notice that XSL resembles XML. In fact, it <strong>is</strong> XML.
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XML takes on many different forms, one is XSL. You might also notice that an
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XSL stylesheet contains XSL templates. An XSL template is a little bit like
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a subroutine or function in other programming languages, and are not to be
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confused with <a href="#XMLTemplates">XML templates</a>. </p>
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<p>The diagram below shows the snippet of XSL that transforms the XML above to
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HTML. </p>
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[[Image:xslsnip.png]]
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===HTML===
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<p>HTML is the format output by the CGI to the browser. It is the result of applying
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the XSL Stylesheet to the XML.</p>
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<p>Take a look at this <a href="search_htmlsource.html" target="_blank">HTML</a>.
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It is the complete HTML source for the Text Class search form.</p>
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<p>The diagram below shows the snippet of HTML generated by transforming the
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XML with XSL. </p>
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[[Image:htmlsnip.png]]
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===Language Map===
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<p>All text that appears as part of the user interface is stored in an XML file.
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Phrases are assigned keys, and the keys are used in the XSL to retrieve phrases.
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The potential exists to have interfaces in different languages. A default map
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resides in the web directory for each Class and is called langmap.en.xml. The
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CGI incorporates the map file into the XML file. </p>
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===Javascript===
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<p>Javascript is another key technology that plays a role in the user interface.
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Like CSS, Javascript is applied by the browser, not the server.</p>
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===Cascading Stylesheets (CSS)===
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<p>DLXS uses CSS extensively to further refine the layout of the HTML. Cascading
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Stylesheets are very different from XSL Stylesheets. XSL Stylesheets affect
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the structure of the HTML document (e.g., the hierarchy of the elements). Cascading
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Stylesheets affect the display of the HTML structure. CSS is great for formatting
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with fonts and colors, and it can even be used to show or hide a portion of
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the HTML. CSS is applied by the browser, not the server.</p>
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===Collection Manager===
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<p>Some of the most common customizations can be done in Collection Manager.
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For example, the title of the collection. Image Class can be customized quite
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extensively in Collection Manager. For example, the display of data fields
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can be configured extensively. Customizations are relatively easy to make in
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Collection Manager. Use it whenever possible. </p>
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===Fallback===
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<p>Fallback is a mechanism used by DLXS CGIs to handle the task of selecting
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user interface files (e.g., XML templates) based on whether the end user is
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working at the class, group, or collection level, and whether user interface
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customizations have been made.</p>
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<p>DLXS allows collection specific user interface customizations.
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Similarly, groups of collections can share a custom interface. The DLXS Classes
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each have a default interface that is used if there are no customizations at
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the group or collection levels. </p>
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<p>When the CGI needs a user interface file, for example, search.xml for the
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text class search form, the Fallback mechanism considers a number of factors
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when choosing a file.</p>
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<ul>
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<li>How many collections are involved? </li>
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<li>Is a group involved?</li>
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<li>Does the file exist
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in the collection's web directory?</li>
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<li>Does the collection have a default
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group?</li>
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<li>Does the file exist in the group's
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web directory?</li>
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</ul>
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<p>Fallback is complex due to the vast number possible situations,
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but has great benefits. It allows very specific aspects of the user interface
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to be customized while all other aspects <em>fall
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back</em> to the defaults at the group or class level. This reduces
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duplication and in the long term minimimizes maintenance work (and the headaches
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that go with it). </p>
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<p><strong>The principle
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idea is to duplicate code as little as possible, and utilize fallback as
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much as possible.</strong></p>
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<p>All user interface files are stored in the file system under <tt>$DLXSROOT/web</tt>. </p>
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<p>There is a directory for files shared across the classes called &quot;lib&quot; and
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located at $DLXSROOT/web/lib. </p>
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<p>Each class has a directory in &quot;web&quot;.</p>
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<ul>
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<li>i/image</li>
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<li>t/text</li>
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<li>f/findaid</li>
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<li>b/bib</li>
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</ul>
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<p>If a group or collection requires customization, it may be necessary to create
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a web directory based on the group or collection ID. </p>
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<ul>
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<li>c/collid (e.g., a/amverse)</li>
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<li>g/groupid (e.g., b/bhl)</li>
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</ul>
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<p>You can see a report of the Fallback file selection process by adding <a href="http://quod.lib.umich.edu/cgi/t/text/text-idx?debug=tpl;page=simple&c=amverse" target="_blank">debug=tpl</a> to
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the URL. The CGI first checks for a file in the collection level directory,
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then group, and finally at the class level. </p>
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<hr size="1" width="90%">
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Next: [[Customizing the User interface]]
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Current revision


[edit] Text Class Behaviors Overview

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