Overview

From DLXS Documentation

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

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[edit] Text Class Behaviors Overview