XML is already being used for #1 and #3 in object-relational mapping products. Here is an example in ObjectSpaces that maps a business object to a relational table.

<map xmlns="http://www.microsoft.com/ObjectSpaces-v1">
  <type name="Customer" dataSource="customers" source="s">
    <uniqueKey name="Id" mappedBy="autoIncrement" dataSource="CustomerId" />
    <property name="Name" dataSource="ContactName" />
    <property name="Title" dataSource="ContactTitle"/>
    <property name="Company" dataSource="CompanyName"/>
    <property name="Phone" dataSource="Phone"/>
    <property name="Fax" dataSource="Fax"/>
    <property name="Orders" relationship="CustomerOrders" side="Parent"/>
  </type>
</map>

As far as #2, I don't think I would ever want to express my application logic with XML/XSLT, but there are standards like the Model Driven Architecture that use XML.

BizTalk is another example that uses XML to express transformations of business documents.

To your point, I can't think of any examples that couldn't be expressed with XML, but still I would want to write my application logic using a good object-oriented language.


>(Also posted in VFP Forum)
>
>I'm under the impression that every piece of application logic that I write is a fancy combination of 3 things:
>
>1. Getting data
>2. Transforming data
>3. Putting data
>
>For example, get some data from a database (1), calculate a total from the data (2), and display it to the user (3), and store the total back in the database (also 3)
>
>If this is all application logic is, using two standards, XML (which includes XSLT) and IP, hypothetically we should be able to get data from anywhere, transform it into anything, and put it somewhere else (or back from where we got it).
>
>Are there examples of business logic that cannot be written as transformations? IOW, Are there examples of applications that cannot be described completely in XML?