XML - An Introduction
Rama as you discovered in the previous page, XML is required for
packaging SCORM-conformant courses, and for content developers, you will need
to prepare this file to describe your course. The good news is that this is not
difficult. The expert level packaging lesson will give you several examples to
work from. However, you will still need to create your own file, and you will
from time to time encounter problems with this file. Here are some essential
for XML.
Tags, Elements &
Attributes in XML
Lets
examine a small part of an imsmanifest.xml file.
Modeling and Simulation
Introduction
and Usage
The
</span></strong>
and <strong><span style="font-family: "Arial","sans-serif";"><item...> </span></strong>syntax
in this xml are called XML "<strong><span style="font-family: "Arial","sans-serif";">tags</span></strong>."
XML tags are always used to begin an XML element. The title of this item, for
example is one<strong><span style="font-family: "Arial","sans-serif";"> element</span></strong>
with the tag <title> and value "Introduction and Usage." An
element, then, consists of a tag and its value.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">An
<strong><span style="font-family: "Arial","sans-serif";">attribute</span></strong>,
has the form name=value, where "name" is a particular variable name
reserved for that element and "value" is the string you want to
associate with that attribute. There are two attributes in this XML:
identifier="ITEM1" and identifierref="INTRODUCTION."
Attributes are used to provide a context to an element.<o:p></o:p></span></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;"></span></font></font><br /></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;">Where is the list of
XML Tags and Attributes that I can use?</span><span style="mso-bidi-font-family: Arial;"><o:p></o:p></span></font></font></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">Which
tags can you use? Well, each XML document has one or more companion files that
define the allowed tags and their attributes. These documents are either <strong><span style="font-family: "Arial","sans-serif";">DTD</span></strong> (Document Type
Declaration) files, with a file type of ".dtd", or they are <strong><span style="font-family: "Arial","sans-serif";">XML schema files</span></strong> with
the file type ".xsd". In SCORM there are four of these files that are
needed. They define which tags can be used in the imsmanifest.xml file as well
as their attributes.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">The
packaging lessons in this course describe the imsmanifest.xml file and the use
of the SCORM schemas in preparing this file.<o:p></o:p></span></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;"></span></font></font><br /></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;">Where do I obtain the
SCORM XML DTDs and Schemas?</span><span style="mso-bidi-font-family: Arial;"><o:p></o:p></span></font></font></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">You
can obtain the SCORM schemas by downloading them from the IMS and ADL web sites
or by clicking on the links in the sidebar of this page. When you click on the
link, your browser will load the schema as a text file. To save it to your
computer, just select "file:save" from you browser's main menu bar.<o:p></o:p></span></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;"></span></font></font><br /></p>
<p>
<font size="3"><font face="Verdana"><span style="color: maroon; mso-bidi-font-family: Arial;">Well Formed &
Valid XML</span><span style="mso-bidi-font-family: Arial;"><o:p></o:p></span></font></font></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">As
mentioned, you will be preparing an xml file to describe the contents of your
course to a Learning Management System or a SCORM repository. In either case,
you will need to ensure that this file (imsmanifest.xml) uses the proper syntax
and that it is valid.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">An
XML file with the proper syntax is called <strong><span style="font-family: "Arial","sans-serif";">"well-formed</span></strong>." An XML file that
is well-formed and also uses the proper tags, as defined by its DTD or schemas
is called "<strong><span style="font-family: "Arial","sans-serif";">valid</span></strong>."
You must ensure that your manifest file is both well-formed and valid before
attempting to load it into a Learning Management System, or into a SCORM
repository. <o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">If
you attempt to load a course with a manifest that is not well-formed or
invalid, then most likely it will fail to load, and worst of all, many learning
management systems will not help identify the problems in your manifest file.
Usually an error message such as "can not parse imsmanifest.xml file"
is written by the LMS to your terminal. It is up to the content developer to
determine why this error has occurred.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">Well-Formed
XML require that 1) every tag be closed, and that 2) tags do not overlap. Here
is part of an imsmanifest file. Notice that the <title> tag is <strong><span style="font-family: "Arial","sans-serif";">not closed </span></strong>since it is
missing a tag:
Introduction
and Usage</span></strong><br />
<strong><span style="font-family: "Arial","sans-serif";"></item></span></strong></span></b><span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;"><o:p></o:p></span></p>
<p>
<br /></p>
<p>
<span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;">The
proper syntax would be:<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<strong><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><item identifier="ITEM1"
identifierref="INTRODUCTION"></span></strong><b><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><br />
<strong><span style="font-family: "Arial","sans-serif";"> <title>Introduction
and Usage
Some
XML elements convey attributes and not data. In this case, there is no need for
a separate closing tag. The following statement is an example of such an
element.
Although
this statement is not closed by a
tag, it is a valid XML
statement that might be found in a SCORM manifest file. Since this statement
only has an attribute associated with it (href=filename), there is no need for
a separate closing tag. These types of XML elements still require closing to be
considered well formed. The closing is done by including the forward slash
character "/" just before the final ">." This is
required. Leaving off that forward slash is not well formed XML since the tag
is not closed, and forgetting to include the forward slash will result in a XML
parsing error.
Well
formed XML must also have non-overlapping tags. A tag introduced after another
tag must be closed before the first tag. In the following example, the
tag should have been closed before the <item> tag because
the <title> tag starts after the <item> tag was introduced. The
<title> tag must be completely nested within the <item> tag, but in
this case it <strong><span style="font-family: "Arial","sans-serif";">overlaps</span></strong>.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<strong><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><item identifier="ITEM1"
identifierref="INTRODUCTION"></span></strong><b><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><br />
<strong><span style="font-family: "Arial","sans-serif";"> <title>Introduction
and Usage</span></strong><br />
<strong><span style="font-family: "Arial","sans-serif";"></item></span></strong></span></b><span style="color: #666666; font-family: "Arial","sans-serif"; font-size: 9pt;"><br />
</span><strong><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;">
Overlapping
tags are not allowed in XML and, in general, will cause an exception from the
LMS or SCORM repository. The correct, non-overlapping XML for the above example
places the closing tag for before the closing tag for
<item>.<o:p></o:p></span></p>
<p>
<br /></p>
<p>
<strong><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><item identifier="ITEM1"
identifierref="INTRODUCTION"></span></strong><b><span style="color: #004040; font-family: "Arial","sans-serif"; font-size: 9pt;"><br />
<strong><span style="font-family: "Arial","sans-serif";"> <title>Introduction
and Usage</span></strong><br />
<strong><span style="font-family: "Arial","sans-serif";">
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