XML: The extensible Markup Language

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Eunice Greer
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1 University of Oregon Applied Information Management Program AIM 610: Managing Information Assets Unit 6, Lecture 1 XML: The extensible Markup Language As we have discussed, it is common wisdom in the IT community that there is a distinction between structured and unstructured content. Structured content is easy to manage in wellorganized repositories such as a relational database. Unstructured content is an unruly mess dumped into arbitrary folders on a file system. While this assessment of unstructured content is most definitely a "glass is half-empty" perspective, there is some validity to it. Information that can be broken into neat, well-defined little chunks, maps very cleanly into the tables and rows of a database and can be manipulated with ease. Free-text, audio, video or composite documents in and of themselves do not fit the model as nicely. As a result, just keeping track of the file is a major accomplishment. Attempting to query the content in any manner beyond full-text search is often considered infeasible. Bringing the power of structured information management techniques to the world of unstructured content has become a central goal of information asset management. However, even if structured information techniques are made applicable to unstructured content, the battle has only begun. Pulling information out of a system is one thing. Putting that information into another system is a different matter all together. It is a simple matter to connect multiple computers and systems, but sharing information in a meaningful way is still problematic. Clive Finkelstein and Paul Aiken make the following analogue to describe the challenge.

2 Every country is now interconnected in a vast, global telephone network. We are now able to telephone anywhere in the world. We can phone a number, and the telephone assigned to that number would ring in Russia, or China, or in Outer Mongolia. But when it is answered, we may not understand the person at the other end. They may speak a different language. So we can be connected, but what is said has no meaning. We cannot share information. Today, we also use a computer and the World Wide Web. We enter a web site address into a browser on our desktop machine a unique address in words that is analogous to a telephone number. We can then be connected immediately to a computer assigned to that address and attached to the Internet anywhere in the world. That computer sends a web page based on the address we have supplied, to be displayed in our browser. This is typically in English, but may be in another language. We are connected, but like the telephone analogy if it is in another language, what is said has no meaning. We cannot share information. 1 Hopefully by this point, you are thinking of ways in which metadata can address this challenge, but that metadata must be structured along with the information it describes in a manner that is digestible by the consuming information system. Providing this structure and the means to interpret it is the role of the extensible markup language (XML). Markup languages like XML allow content to be separated from its presentation, which gives you tremendous flexibility in how that content is to be managed. This separation of content and presentation is most familiar in the form of the HyperText Markup Language (HTML), which encodes most of the content currently available on the World Wide Web. By tagging content, such as <emph>emphasize this phrase</emph>, the author can indicate that the enclosed content is to be given special processing. The consumer or rendering mechanism, for example a web browser, word processor, printer, etc., can then be programmed to interpret that instruction. One web browser may display the phrase as emphasize this 1 Finklestein, C. and Aiken, P., Building Corporate Portals with XML (McGraw-Hill, 1999), p. 24. Managing Information Assets Unit 6, Leacture 1 Page 2

3 phrase, while another renders it as emphasize this phrase and yet another chooses to display emphasize this phrase. While this tagging process is useful in describing web pages, it is still too restrictive in that we are constrained by the tags that are defined as part of HTML. They are also not particularly useful in describing information that is to be exchanged between databases and information systems. For example, how would you encode a bit of data representing transmission time, access privilege, or session length in html? The ability to define our own descriptive tags, tailored to our specific needs for content description and management, would be more useful. This was the idea behind the Structured General Markup Language (SGML), the predecessor to XML. SGML was intended as an all-encompassing markup language for defining markup languages. Both HTML and XML are defined in SGML. As a result of its broad scope, SGML proved too cumbersome for use as a work-a-day markup language for information description and interchange. This led to the birth of XML, which emphasized the extensible nature of SGML while reducing its scope to a more manageable level. The central mechanism of XML (and SGML) aside from the tags themselves, is the Document Type Definition (DTD), although these are starting to be replaced by the more versatile schema. The DTD defines the rules of how a particular type of document may be put together in terms of what elements may be included, how often and in what order. Managing Information Assets Unit 6, Leacture 1 Page 3

4 A Simple DTD with XML 1.0 Coding <?xml version="1.0" encoding="utf-8" standalone="yes"?> <!DOCTYPE BOOK [ <!ELEMENT BOOK (TITLE+,AUTHOR+,ISBN+,PRICE,DESCRIPTION)> <!ELEMENT TITLE (#PCDATA)> <!ELEMENT AUTHOR (#PCDATA)> <!ELEMENT ISBN (#PCDATA)> <!ELEMENT PRICE (#PCDATA)> <!ELEMENT DESCRIPTION (#PCDATA)> ]> <BOOK> <TITLE></TITLE> <AUTHOR></AUTHOR> <ISBN></ISBN> <PRICE></PRICE> <DESCRIPTION></DESCRIP TION> </BOOK> This DTD describes a document of type book that consists of one or more TITLES, followed by PRICE followed by one and only one DESCRIPTION. A more or less equivalent XML Schema is below. <xs:schema xmlns:xs=" <xs:annotation> <xs:documentation> A sample XML Schema. </xs:documentation> </xs:annotation> <xs:element name="book" type="booktype"/> Managing Information Assets Unit 6, Leacture 1 Page 4

5 <xs:complextype name="booktype"> <xs:sequence> <xs:element name="title" type="xs:string" minoccurs="1" maxoccurs="1" /> <xs:element name="author" type="xs:string" minoccurs="1" maxoccurs="1" /> <xs:element name="isbn" type="xs:string" minoccurs="1" maxoccurs="1" /> <xs:element name="price" type="xs:string" minoccurs="1" maxoccurs="1" /> <xs:element name="description" type="xs:string" minoccurs="1" maxoccurs="1" /> </xs:sequence> </xs:complextype> </xs:schema> The syntactic rules of XML are pretty straight forward. XML documents along with their tags are composed of strings of Unicode characters. Anything that is supposed to be processed by an XML parser, the mechanism that chops up and manipulates the document according to your XML instructions, needs to be prefaced with either a less-than character < or an ampersand &. These are signals to the parser that this is something it needs to pay attention to. Anything else is treated as simple character data and is ignored. Think of this like a document in a word processor. The application doesn t care whether you are writing a grocery list or the Great American Novel. The only things it cares about are only visible if you turn on the reveal codes feature. Now you see the paragraph marks, the bold indicators, font markings and section breaks. XML tags are the equivalent of the document processing codes only much more flexible. A few rules do apply to these tags and instructions. First, they are case sensitive. <ADDRESS> is not the same as <Address> or <address>. As far as the parser is concerned, these are three separate, distinct and unrelated tags and will be treated accordingly. White space characters, such as space, tab, character returns and the like, are Managing Information Assets Unit 6, Leacture 1 Page 5

6 valid but not meaningful to the parser. Feel free to use them liberally to prettify your XML documents and to make them more readable. In fact, most XML tools offer a beautify function that uses white space to make the document more friendly. Another important concept is that of names, name characters and name tokens. You need to label things within XML, that is give them names, and of course there are rules for doing this. Any Unicode character is valid for use in an XML name unless it is included on the official list of punctuation characters which include the tilde ~, space and caret ^ among others. Most of these can be used anywhere in an XML name including its beginning and are called name start characters. As Goldfarb points out, the existence of name start characters implies the existence of characters that are not valid at the beginning of a name. These include numbers, hyphens and a period. These can be used in the name, but may not be its first character. This group is called the name characters. Now that you have all the rules for XML names you may disregard them. Name tokens do not treat the first character as special. So ~6.45.info.asset.lecture.6^1 is a name token but not a name and this.is.a.name is both. Name tokens can be useful in the same way the variables are useful in programming languages or for specifying that non-name characters are legal or even necessary in certain places within a document. 2 To get a full understanding of the rules of DTD, Schema and tag creation, your best source is the XML specification itself, which is available from W3C. ( The document itself (and by document, I mean any container of information or data) is marked up with the tags defined in the DTD to demarcate where a particular element begins and ends. With this paring of document and DTD, the content becomes self-describing, which allows any mechanism to process the document as intended by the author. The 2 Goldfarb, C., The XML Handbook (Prentice Hall, 1998), p. 771 Managing Information Assets Unit 6, Leacture 1 Page 6

7 document is parsed by the application, breaking it up into its constituent parts according to the rules specified in the DTD or schema, into a common tree representation that may then be accessed by common methods regardless of the nature of the tool or application being used. This provides as gross or fine a level of granularity as the author of the document or DTD desires. Rather than just managing a document as a single, monolithic file, the DTD allows mechanisms to deal with it in terms of individual components, including chapters, pages, paragraphs, words or whatever unit is defined. It is this aspect of information markup that is making XML the lifeblood of Information Asset Management. Once properly tagged, the information asset or any of its components can be processed as efficiently and with as much versatility as any database record. XML is readily machine-readable in contrast to most unstructured information, which must first be extracted into separate metadata in order to be processed. This may seem to be much ado about nothing much, but consider the ramifications in terms of information single sourcing, reuse and repurposing. McDonald s Corporation provides an interesting case in point. Until recently, McDonald s provided content to 1.6 million users in 119 different countries without an overarching content management strategy or repository. As a result, a single product would be photographed countless times by various franchises around the world at an average cost of $10, per photo session. When users attempted to share or reuse content, network bandwidth was taxed, servers were swamped and version control became all but impossible. 3 By implementing AccessMcD, even with only limited XML, McDonald s was able to provide two common content repositories to its global community. There was a definitive image of a Big Mac that could be used in any number of circumstances. When 3 See Michael Voelher s article Reusing Content Without Starting from Scratch. Intelligent Enterprise, June, Managing Information Assets Unit 6, Leacture 1 Page 7

8 a customer in New Delhi wanted nutritional information, they could receive the same information as a customer in New Jersey. A corporate approved blurb on founder Ray Kroc could be located, retrieved and inserted into a press release, a place mat or a newspaper ad. A smaller section of the same press release could also be retrieved in multiple languages for international advertising, allowing not only for reuse, but also repurposing based on the locale tag. Document description can go far beyond structural tagging. Semantic tagging can radically improve the accuracy and efficiency of search and retrieval. With traditional, Googlesque full-text searching there is no way to indicate which meaning of a particular term you are searching. A query on the term Washington could return references to a State, a Statesman, a Capital or a type of apple. However if the content is tagged to indicate the use of the term, our search capabilities increase dramatically. <StateName>Washington</StateName> <Fruit>Washington Apple</Fruit> <City>Washington</City> <ProperName>Washington</ProperName> Not only can we indicate that it is the State of Washington for which we are looking, we can specify that we are looking for documents that contain Washington in the Heading of a Particular Subsection of a Particular Chapter and retrieve only that chapter. Other Managing Information Assets Unit 6, Leacture 1 Page 8

9 technologies in the XML family, such as XPath and XQuery, facilitate this type of retrieval. We will discuss them along with XSLT in the next lecture. An additional side benefit of full utilization of the extensible Markup Language is compliance. As regulation and oversight become increasingly burdensome, content markup is being leveraged to meet compliance obligations. For example, the Food and Drug Administration (FDA) is adopting an XML-based pharmaceutical labeling system: Structured Product Labeling (SPL). By mandating adoption of SPL, the FDA is attempting to promote accurate and expeditious data interchange and document sharing among various members of the pharmaceutical industry, care providers and the agencies that regulate them. This also gives content management system developers, vendors and managers a standard for developing organizational schemes, which will support internal information management as well as interchange. Managing Information Assets Unit 6, Leacture 1 Page 9

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