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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>
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<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>

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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

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Questions & Answers

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
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it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
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what is biological synthesis of nanoparticles
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what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
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Source:  OpenStax, Connexions tutorial and reference. OpenStax CNX. Feb 23, 2012 Download for free at http://cnx.org/content/col10151/1.27
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