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This module describes XML (eXtensible Markup Language) and the rules that govern its usage. It also explains what a well-formed and valid document is.

What is xml?

The eXtensible Markup Language ( XML ) is a meta-markup language defined by the World Wide Web Consortium (W3C) . It is not strictly a markup language itself, but rather a set of rules for creating markup languages. Forour purposes a markup language is any language (HTML, for example) that uses tags surrounding text to conveyinformation such as content or format. CNXML , the markup language used by the Connexions Project is an example of a language written in XML. There are many otherexamples at the W3C site. Here is an example of some markup in CNXML.

<para>This is a paragraph in<term>CNXML</term>. Notice that the markup contains tags that express the meaning of the text.</para>

<para> and </para> are the tags that enclose the text. In XML, tags are always marked by anglebrackets (also known as < and > ). Tags generally come in pairs. An opening tag will look like <tagname> . A closing tag will look like </tagname> , with a / preceding the tag name.

XML allows the separation of presentation from content. For example, HTML has tags such as <u> and <i> , which underline and italicize text respectively. This does not express content information,only formatting. XML allows you to define your own language of tags to represent content. You could create a tag called <book> to represent book titles, and create a stylesheet (a separate formatting document), thatsays that every <book> tag should be italicized or underlined. Then when you want to change thepresentation of that type of content, you just change one small part of the stylesheet. Also, if you make tags thatconvey the content of the document, you can enable better searching. For example, you might look for the author of a document by looking at the author tag.

Well-formed xml

XML has a few rules that apply to all of its languages, including CNXML. If a document satisfies theserules, then it is well-formed . XML documents are required to be well-formed.

  • Every tag that is opened must be closed. An opening tag looks like <module> and a closing tag looks like </module> . There is a shortcut. If your tag contains no other tags (referred toas an empty tag ), then you can can type a / before the end of the opening tag and delete the closingtag. For example, <media></media> can be abbreviated <media/> .
  • Tags must be nested within each other. So, <b>red<i>and</i>blue</b> is fine, but <b>red<i>and</b>blue</i> is incorrect because the <b> and <i> tags have overlapping content.
  • You must put either single or double quotes around an attribute value. An attribute is some sort of information that is associated with a tag and is listedinside of the tag itself. For example, <module id="m0001"> and <module id='m0001'> are fine, but <module id=m0001> is incorrect.
  • You can also choose to start every document with an XML declaration . If you do use the XML declaration, then it has to be the very first thing in thefile. It cannot even be preceded by whitespace. It is not considered to be a tag. The XML declaration is asfollows. <?xml version="1.0"?> You can also include other information such as the encoding of the document or whether the document dependson other files or not.
  • There must be one tag that contains all of the other tags. For example in xhtml <html> and </html> must surround all of the other tags. There are some things that are includedat the top of the document that are not tags and that are not included with the tags. The XML declaration is anexample of this.

Valid xml

It is possible to define a set of rules that apply to all of the tags in a particular XML language. These rules can bedefined in a couple of different ways. The most common way is to use a DTD (Document Type Definition). Any document which follows all of the rules for that language iscalled valid . A document is not required to be valid in order to be XML. However, it is generally a goodidea.

Entity references

Entity references in cnxml 0.6

Entity references are no longer supported by CNXML 0.6. Instead, we suggest that you use character references as described below to add special characters to your module.

XML uses several characters in special ways as part of its markup, in particular the less-than symbol ( < ), the greater-than symbol ( > ), the double quotation mark ( " ), the apostrophe ( ' ), and the ampersand ( & ). You've already seen examples of markup using the first four of those previously in this module.But what if you need to these characters in your content, and you don't want them to be treated as part of the markup by XML processors? You can use XML entity references for this purpose. The XML Specification defines the following five entity references for use in any well-formed XML document:

  • &amp; refers to an ampersand (&)
  • &lt; refers to a less-than symbol (<)
  • &gt; refers to a greater-than symbol (>)
  • &quot; refers to a double-quote mark (")
  • &apos; refers to an apostrophe (')

Suppose you have a document with the following: <para id="p1">The firm was known as Scrooge and Marley.</para> you could replace 'and' with the entity reference &amp; : <para id="p1">The firm was known as Scrooge&amp; Marley.</para>

All entity references outside the above five must be defined in a document type declaration, and they may only be used in documents that conform to that DTD. Note that an entity reference always begins with & and ends with ; .

Character references

You can also use any character defined in Unicode in an XML document by means of character references . Unicode is a project to define a unique code for everycharacter in any human language. Unicode is very useful any time that you need to use a symbol that is not a part ofASCII.

Character references in XML either begin with &# , or they begin with &#x , and they end with a semicolon ; . A character reference contains a representation of a Unicode code point: if it begins with &# , then it contains a decimal representation of a Unicode code point; if it begins with &#x , then it contains a hexidecimal representation of a Unicode code point.

The hexidecimal representation of the Unicode code point for the small 'o' with a stroke is 00F8 , and the decimal representation for the same is 248 . Therefore, the character references for the small 'o' with a stroke are &#x00F8; and &#248; So you could write <emphasis>The majestik m&#x00F8;&#x00F8;se</emphasis> or <emphasis>The majestik m&#248;&#248;se</emphasis> or even <emphasis>The majestik m&#x00F8;&#248;se</emphasis> to get

The majestik møøse

Questions & Answers

are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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Source:  OpenStax, Cnxml tutorial. OpenStax CNX. Jul 08, 2009 Download for free at http://cnx.org/content/col10121/1.10
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