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 Towards the semantic web II

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The concept map (or semantic network) and the XML language

What is XML?

XML is a language, a language designed to describe the structure of an entity, of a document: a text, a table, a data base, a video, an image, a concept map, a semantic network, a bank transaction, the population registry, a knowledge base, a web site... A document structure can be simple or complex.

XML, as the document internal structure carrier, has two main functions:

punto elenco The exchange of contents between applications
punto elenco Direct access to contents, in plain text format, still "readable" by humans.

The main goal of XML design has been to endow the Web with semantics.


How is the map ported to an XML structure, what does it contain and how is it represented?

Being the concept map essentially a cognitive and logical structure (graphics is only a circumstantial and visual consequence of that structure), in the resulting XML file a logical and cognitive structure of the map through its fundamental components will be reproduced:

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Nodes (internal and external concepts)

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Categories with which concepts are qualified (concept types)

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The graphic aspect of these concept types

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The relations between nodes

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The relation types that qualify those relations

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The descriptive texts of concepts

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The authors' map description

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The dimensions or contexts of the map

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An evidence of external associations

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For a recapitulation, the Knowledge Master XML export also contains a structured list of propositions

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And other descriptive elements as well.

Thus, a concept map (or a semantic network, or knowledge base) can be exported to XML and then its semantic structure "read" by a database management system, like Access or Oracle, or imported in a word processor or handled by another system based in some other knowledge management paradigm (visual or not).

An example of an XML file segment presenting the minimal description of a concept.

<InternalConcept id_IntCnpt="19895" posX_Int="228" posY_Int="51" AsImage_Int="false">

<IntCnptName>the eye</IntCnptName>
Type>sensitive organ</Type>


Tags are enclosed between the symbols '<' and '>' and tags enclose data.

Some simple observations about XML
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As XML can be used to describe other languages, it is considered a metalanguage;

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Among markup languages, XML is a "brother" of HMTL, being both "children" of SGML. XML complements HTML, more than replacing it, because HTML has the only function of presenting data, while XML represents the contextual meaning of data;

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XML is verbose, and files in this format tend to be big;

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XML is a family of languages... ever growing;

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XML is a WWW standard;

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XML is a flat text file, that can be read (or observed, analyzed) with a simple note pad or with a web browser;

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XML is also used as vector in instant messaging, and in the immediate future it will be very difficult to find applications that do not manage contents exchange through XML;

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XML means eXtensible Markup Language, it means that anyone can extend it by creating tags of their own, it does not have a fixed format;

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Being an open text format, it is platform independent, it can be ported to any computer or OS;

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XML files can be used for storage, processing or transmission.

Some insight about XML

1. XML is a method to place structured data in a flat text file

Structured data are those that can be organized in fields, for instance an address book, a table, a data base, a semantic network or concept map, a knowledge base, and so on. Often these data are managed in binary format, non understandable by people, rendering necessary the original program (or a similar one to decode it) to be able to access contents. XML is a tagged text format, it is, even if this is not its goal, it can be "read" and controlled by a person. XML is a set of rules, directives and conventions to design text formats for these data, so as to produce files that can be easily generated and read (by the computer) unambiguously, and that avoids traps as the lack of extensibility or internationalization.

2. XML looks a little like HTML but it is not HTML

As HTML, XML uses marks (tags) (words delimited by '<' and '>') and attributes (with the form name="value"), but while HTML specifies the meaning of every mark and attribute, and often the way it appears in the browser), XML uses tags to delimitate data elements, and leaves fully the interpretation of data to the one that reads them. In other words, if we see a " in an XML file, it doesn't necessarily mean that it is a "bold" sign. Dependent of the context, it can be binding, a bonus and even it isn't related to a word that starts with a "b".

3. XML is a text, but it is not designed for "reading"

XML files are text files, but these are not intended to be read by people, even less than HTML files. These are text files because they enable the experts (for instance programmers, and knowledge workers) to control applications, and in an emergency use a word processor to fix an error. But the rules for an XML file are much more rigorous than for an HTML file. A forgotten tag or simply a wrongly placed quotation mark (") render the file useless. On the contrary of what happens with an HTML file, when an application find an error in an XML file, emits an error message and stops "reading" or importing.

4. XML is a family of technologies

There is XML 1.0, the specification that defines what are the tags and attributes and how they are, but around XML 1.0, there is also a set of optional modules that offer specific tags and attributes or directives for specific tasks. There also exist Xlink, XPointer and XFragments; CSS, the style sheet language is also applicable to XML as it is to HTML. XSL is the advanced language to style sheets. RDF (Resource Definition Framework), the standard WWW metadata, offers a grammar and syntax to enable sharing the description of resources and to ease the interoperability between applications. There are many other developments, but what results specially interestingis its derivate XML ("topic maps" or could be better "contents maps", see), specially devised for the description, navigation and exchange of associative information, just like concept maps, semantic networks, knowledge bases, frames systems, etc. This is the specific format to exchange contents between applications that manage knowledge structures or analogous associations.

5. XML is verbose, but that is not a problem

Being XML a text format that uses tags to delimitate data, an XML file usually tends to be big. At the same time also disks have this tendency, and however there exist programs to compress these files. Even modems can also compress files on-line, as also do protocols for data transmission in the web.


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