Week 9 Readings

I have absolutely no experience or knowledge of XML so these articles were very helpful to me, though sometimes a little too technical for me to understand. I seem to have a much better understanding of how to use XML, but am still unclear on a few things that will hopefully be talked about in class.

1.)Bryan, "Introducing the Extensible Markup Language (XML)"

XML is a subset of the Standard Generalized Markup Language (SGML), and is designed to make it easy to interchange documents over the Internet. With XML you must always clearly defined your start and end, as opposed to HTML where it is sometimes acceptable to not close your end tag. XML Document Type Definition (DTD) can be used to check to make sure that components of the XML document appear in a valid place.

XML is based on a concept of documents composed of a series of entities (things or objects); each entity can contain one or more logical elements, which can have attributes. One of the interesting things about XML is the way it incorporates special characters into the code, I liked how it did this.

An XML file has three types of markups - the first two are optional. First, the XML processing instruction, which identifies the version of XML being used. Second, the document type declaration. Lastly, the fully tagged document instance. If all three are present then the document is considered "valid." If only the last one is present then the document is "well-informed." XML is ideal for using in databases.

2.) Uche, "A Survey of XML Standards"

I liked how this article was setup and that it provided you with a brief overview of many diffrent parts of XML and what they can do - not just technical information on how to use/write XML

XML has been widely translated to different languages, but English is still the standard. There was some controversy when XML 1.1 came out. This new version had only very small changes to it and people wondered whether a new version was really necessary, especially because there was a good chance interoperability issues would arise.

XML catalogs define the format for instructions on how the processor resolves the entities into actual documents. XML namespaces proved a mechanism for naming elements and attributes. Xinclude is still being developed, but it will provide a system to merge different XML documents. This is usually used to split large documents into manegable chunks, then merged back together again. Xpath can be used to locate certain elements in a document. Xlink is a generic framework for expressing link sin XML.

3.) Bergholz, "Extending Your Markup"

I really liked the figures in this article, they provided good examples of XML. The examples were complex enough that you got a decent idea of how to write XML, but not so complicated that you didn't understand what they were trying to portray.

XML is all about meaningful annotations. DTD's define the structure of XML documents; they specify a set of tags, order of tags, and attributes associated with tags. XML elements can be either terminal or nonterminal. Nonterminal elements contain subelements which can be grouped as sequences or choices. XML attributes use the !ATTLIST tag.

XML extensions include namespaces and addressing and linking abilities. Unlike HTML it is not necessary to use an anchor in XML, and extended links can connect multiple documents together. Namespaces avoid name clashes. Extensible Stylesheet Language (XSL) can allow you to transform XML into HTML. XML schema allows the user to define datatype.

4. W3 Schools Tutorial - XML Schema

Much like the HTML tutorials the XML tutorial was very helpful; I really like the W3 school tutorials, and their website. I wish this website would have given more technical information on how to actually write XML schemas (like it did with HTML) as opposed to more theory, or what XML schema can do.

XML schema describes the structure of an XML document and can be used as an alternative to DTD's, as they are much more powerful. XML schema defines elements, attributes, order of elements, and many other things. It supports datatypes and is written in XML, which has many advantages to it. A simple element contains only text, and cannot have attributes. If a element has an attribute it is considered complex. Restrictions can be used to define acceptable values for elements and attributes.

A complex element contains other elements and/or attributes. There are four kind of complex elements. Empty complex elements - they can't have contents, only attributes. Elements only - contains an element that contains other elements. Text only - can contain text and attributes. Mixed - can contain attributes, elements, and text. Indicators control how elements are to be used. String data types are used for values that contain strings.

After reading the articles I have a much better understanding of XML. One thing I'm still confused about though are the advantages of XML over other markup languages, specifically HTML. A lot of the articles stated that XML was better and gave theoretical reasons why it was better. From looking at the many examples of things being written in XML it looks enourmously more complicated than HTML though. Something can be written in HTML in a few lines looks like it takes a ton of lines in XML. I know XML is suppossed to be better than HTML it just looks way more complicated and time consuming.