When should I use xml schemas(.xsd) when reading xml?

Question

Hi,

I have a XML file which holds configuration data for data sources, and the related queries held in 'dataseries' elements.

As I don't really need domain objects made up from the XML, rather just settings read and used to configure connections etc. I was wondering if there is any advantage in using the XML schema I have defined?

I am using LINQ to XML for reading my XML and initially thought it would be a good idea to use strongly typed XML.

Should I be using the .xsd or is it overkill?

A mock XML file:

 <?xml version="1.0" encoding="utf-8" ?>
<datasource name=" Datasource" cache="true">
  <database>
    <connection>
      <provider-name>sqlServer6.0</provider-name>
      <source name="E5"
            connectionString=""/>
    </connection>
    <update-interval>30</update-interval>
    <minimum-update-interval>2</minimum-update-interval>
  </database>
  <dataseries name="" identifier="e5">
    <graph-type></graph-type>
      <query>
        SELECT Period, Price
        FROM PriceUS
        WHERE Date = @date
      </query>
  </dataseries>
  <dataseries name="" identifier="e52">
    <graph-type></graph-type>
    <query>
      SELECT Period, Price
      FROM PriceUS
      WHERE Date = @date
    </query>
  </dataseries>
</datasource>

Answer 1

A schema is good when you want to validate the XML, for example, ensure that certain elements are present or have a limited set of values. A schema is also good if you will be doing a lot of work with the XML and it would be easier to convert the XML into C# objects -- in this case you can use the xsd.exe code generator to generate C# objects that can be marshaled and unmarshaled from the XML.

Answer 2

There are two levels of "correct" XML documents: well-formed and valid. Well-formed means it conforms to XML spec, and valid means that it conforms to your schema. If and when you are accepting an XML document from a total stranger, it's usually a good idea to check the validity of the document before moving forward.

As you mentioned, XML schema could also be used to generate XML databinding entities. When you publish a service or a schema to the world or your client, the schema document could be used as a spec. The world or your client can then use the XSD file to validate or databind to XML documents that you exchange.

Answer 3

Technically, there are two formal schema types in XML. There's the original schema syntax, called a Document Type Definition (DTD), which is a holdover from the ancient SGML days. And then there is the W3C standard, XSD, which is more compatible with modern data.

The only reason I mention this is that you might receive an XML file that is described using a DTD and you might need to know how to deal with it.

But please, friends don't let friends create DTDs for new applications.