Introduction to XML in Flash
       by senocular

Evaluation: XML And Your Family Tree
I've been ranting on an on throughout that XML seems fit for a family tree. Parents, children, siblings - XML just seems so very family oriented. But is that really the case? Lets take a closer look at how elements in an XML hierarchy are arranged and whether or not they make presenting a family tree easy.

Way back when, the file-folder analogy was used to help describe the structure of XML. You have folders (elements) and in those folders you have files or more folders (elements and other child nodes). Any single folder can have any number of files or folders and any of those folders within a folder can have their own similar collection and so on. A file or folder, however, only exists in a single folder at any given time. You get a relation that looks like this:

[ general structure of xml ]

Because everyone can relate to their family and know who's who (who's a parent and who's a child), keywords used to describe similar relations are used to make using XML more comprehensible - child nodes, parent node... siblings, etc. However, if you think about it, they aren't quite exactly the same. There's one key difference in the real family structure when compared to that of XML. That difference is having two parents. Look at the following. It represents a portion of the family structure of a single person (subject)

[ structure of a family tree ]

Here, the subject belongs to two parents, a mother and a father. The children belong not only to the subject, but also to the subject's spouse. So the children, too, have more than one parent. Like with files and folders, this just isn't possible with XML (that's right, XML does not support multiple inheritance). This doesn't, however, make an XML version of a family tree impossible. It just makes it so that an XML representation will not structurally match the content it contains. And there's nothing wrong with that. It's perfectly fine but it also means that interpreting that information will might take a little more effort.

An example would be... wouldn't you know it, FTML. Yup, Family Tree Markup Language - XML for family trees (FTML is technically based off of SGML like HTML and XML). FTML uses id attributes to manage and relate people to other people as they are linearly listed within a FTML document. Take a look at this quick example:


<?xml version='1.0'?>
<!DOCTYPE ftml SYSTEM "ftml.dtd">
<person id="Granddad" sex="male" surname="Example" forenames="Granddad">
<born date="1915" />
<died date="1998" />
<person id="Grandma" sex="female" surname="Jones" forenames="Granny" />
<person id="Dad" sex="male" surname="Example" forenames="Daddy">
<born date="1940" />
<mother id="Grandma" />
<father id="Granddad" />
<person id="Mom" sex="female" surname="Smith" forenames="Mommy" />
<person id="Uncle" sex="male" surname="Example" forenames="Uncle" />
<person id="Aunt" sex="female" surname="Trotter" forenames="Aunt" />
<person id="Me" sex="male" surname="Example" forenames="Me">
<born date="1973" />
<mother id="Mom" />
<father id="Dad" />
<person id="Brother" sex="male" surname="Example" forenames="Brother">
<born date="1971" />
<mother id="Mom" />
<father id="Dad" />
<marriage husband="Dad" wife="Mom" date="1964" />
<marriage husband="Uncle" wife="Aunt" />


All people within this family structure here are listed linearly in the people element. Each person is given an id which is then referenced in two places: 1) in the person definition where a mother and/or father is specified and 2) in the marriages section where a husband and wife are connected by id (some versions of xml-based family trees keep marriage relations within the person tag under wife or husband).

So, the best use of the XML hierarchy within this document is just maintaining content concerning a single person (and the collection of people). Actual relations are all handled through ids. So despite my hopes in creating an example based on a family tree, given the type of XML design needed above, that's not something we're about to tackle here. Lets continue with another, simpler example. For your own XML projects, however, you may need to consider a setup something similar to FTML. Something to keep in mind.


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