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I have an xml file format that looks something like this:

<topLevelTag>
  <category name="foo">
    <item attrib="value">ItemName</item>
    <item attrib="value2">AnotherItem</item>
  </category>
  <category name="bar">
    <item attrib="value">ItemName</item>
    <item attrib="value2">AnotherItem</item>
  </category>
</topLevelTag>

The code that parses this creates an instance of ItemName and is told that it's one category is, in the first case, "foo", and then creates a second instance of ItemName which has associated category "bar".

The problem is that I need to redesign the system so that each Item can have more than one Category. But I still need to be able to create multiple items as well. For example (using bullets instead of xml) I might need to create the following instances:

  • ItemName
    • Primary Category - "foo"
    • Secondary Category - "bar"
  • ItemName
    • Primary Category - "bar"
    • Secondary Category - "foo"
  • ItemName
    • Primary Category - "foo"
    • Secondary Category - "quux"
  • AnotherItem
    • Primary Category - "baz"
    • Secondary Category - "foo"
    • Tertiary Category - "monkey"
    • etc ... (no cap)
  • StillAnotherItem
    • etc ...
  • etc ... (no cap)

How can I design my XML format to encapsulate this many-to-many relationship?

I am aware this question is on the borderline between StackOverflow and Programmers. I chose to put it here because it is a software architecture and design question. If not please let me know and I'll be happy to move it. Precedent one | Precedent two | Precedent three

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durron597
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1 Answers1

3

Why can't you use the same structure as in your bullets?

<topLevelTag>
    <item id="1">
        <value>ItemName</value>
        <category level="primary">foo</category>
        <category level="secondary">bar</category>
    </item>
    <item id="2">
        <value>ItemName</value>
        <category level="primary">foo</category>
        <category level="secondary">bar</category>
    </item>
</topLevelTag>

(the "id" distinguishes two instances of the same itemName).

For sure, you can't have a "many to many" structure explicitly - you must pivot (root?) either on item, or on category, since you need a hierarchical data set.

Or you change completely layout and pivot on the many-to-many relationship; this is easiest to convert to and from a RDBMS storage.

<topLevelTag>
    <item id="1">...</item>
    <category id="1">foo</category>
    <mapping>
        <map item="1" category="1" />
        <map item="1" category="2" />
        <map item="2" category="2" />
    </mapping>
</topLevelTag>
LSerni
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  • Can you explain and/or provide a link as to what you mean by "pivot"? – durron597 Mar 24 '15 at 13:55
  • I am sorry, I am translating - English is not my native language, and I sometimes make up words. What I mean is that one type of node ("item") must be above and have "category" below, or vice versa; in the first case I would say that the structure is... *hinged*? on items, in the other, on categories. In the last example I'm using the term improperly, as all three entities are instances of something which is no longer a topLevelTag, but perhaps a collection, or a table. – LSerni Mar 24 '15 at 13:59