|ceXML - an XML vocabulary for building and civil engineering: Master thesis|
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In the section called General working of XML, information was tagged with nametags. In order for computersystems to understand those tags, it is necessary to define beforehand which tags are allowed. This enables computersystems to decide which action to take when confronted with an <orderform> tag (namely, feeding it to the order processing part). In an analogy to human speech, the specification of the language is called a vocabulary. In XML terms, this vocabulary is called an XML schema or an Document Type Definition (DTD).
The language you speak electronically is both enabled and restrained by the vocabulary. A big vocabulary with very loose grammar results in rich expressive possibilities, but on the downside, it results in hard-to-understand messages. The opposite is true also. A small vocabulary with strict rules allows you to communicate only a limited scope of messages, but the messages are very clear to understand. How to proceed? Designing a vocabulary is a difficult task. That is why the upcoming Chapter 5 looks at three existing initiatives for good current practice in designing vocabularies.