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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Simple Question
 Ramkumar Menon wrote: > What was the fundamental motivation for having attributes in an XML > Document ? Whatever that can be contained in an attribute of an > element can be contained within a sub element. If I model an XML > Document as a Java object, would I need to distinguish between the > elements and attributes ? Moreover, why was it decided that attributes > can only be of a simple type ? Attributes were one of the big step forwards that SGML brought over "Gencoding", one of the previous formats in the 70s. Consider the following questions: "Why should batch files or shell commands have arguments, when all information can be put through standard input/output?" "Why should functions or methods have more than one argument, when all arguments can be put into a single object, and (perhaps) all functions Curried to accept single arguments anyway?" "Why should natural languages have adjectives, when everything can be described using verbs, nouns, adverbs etc.?" "Why is context (path, font, position) important for keeping track of the signifance of some information in relation to other information?" I believe the answers to each of those questions also applies to XML. The answer boils down to human amenability: there is a profound human factors reason why the versions of LISP that succeeded had keyword arguments and putprop/getprop (or equivalents), and why commands in shellscripts/batch files take arguments. People understand things having named properties, and they appreciate it when there is a way of differentiating between the properties of a thing and its parts or holders. An element name is a function (ultimately defined by the recipient as a relation, semantic or presentational function) over its contents, and attributes parameterize this function. Attributes are a theory about which simple types will be used by recipients to handle their contents. It is encapsulation; it says "to use this element, you generally will need to also know some of these attributes; however you generally don't need to know the contents or their attributes." If you view XML as a way of sending relational data from A-B, none of this probably will matter to you. But XML was not designed primarily to send relational data. Cheers Rick Jelliffe 
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