Data description language for record based systems

1. In a computing environment, a method of determining compatibility of typed data structures that conform to the Extensible Application markup Language (XAML), the method comprising:

accessing a first typed data structure defined in a mark-up object of a first type, the first typed data structure comprising a first plurality of fields, wherein each of the first plurality of fields defines a member of the first type consisting of one of a property, a method, or an event of the first type, wherein each member has a name and a type;

accessing a second typed data structure defined in a mark-up object of a second type, the second typed data structure comprising a second plurality of fields, wherein each of the second plurality of fields defines a member of the second type consisting of one of a property, a method, or an event of the second type, wherein each member has a name and a type;

comparing the first typed data structure to the second typed data structure to determine if the first and second types are compatible, wherein the comparison is performed by comparing the members of the first typed data structure to the members of the second typed data structure; and

determining based on the comparison that the first type is compatible with the second type if for each member in the first typed data structure, there is a member in the second typed data structure that has the same name and a compatible type.

2. The method of claim 1 , wherein at least one of the first type or the second type is a description comprising an instantiation of a type.

3. The method of claim 1 , wherein at least one of the first or second plurality of fields comprises at least one of an element or an attribute.

4. The method of claim 1 , wherein at least one of the first or second plurality of fields comprises both an element and an attribute.

5. The method of claim 1 , wherein at least one of the first or second plurality of fields comprises a property identifying the first or second type as a value type such that identity is not preserved for multi-referenced instances.

6. The method of claim 1 , wherein at least one of the first or second plurality of fields comprises a property identifying the first or second type as a reference type such that identity is preserved for multi-referenced instances.

7. The method of claim 1 , wherein at least one of the first or second plurality of fields comprises a property identifying the first or second type as nullable by specifying a value may be represented by a null construct.

8. The method of claim 1 , wherein comparing the first typed data structure to the second typed data structure comprises comparing fields appended to the first typed data structure from a type external to the first typed data structure, to the second typed data structure.

9. The method of claim 1 , further comprising, nominally determining compatibility of the first and second typed data structures by comparing a name of the first typed data structure to a name of the second typed data structure.

10. The method of claim 1 , wherein determining based on the comparison that the first type is compatible with the second type comprises determining that an in-memory structure conforms to a particular description.

11. The method of claim 1 , wherein determining based on the comparison that the first type is compatible with the second type comprises determining that a serialized form conforms to a particular description.

12. The method of claim 1 , wherein comparing the first typed data structure to the second typed data structure to determine if the first and second types are compatible further comprises:

determining that the first and second typed data structures each have the same values defining the nullability, identity and referenceability of their respective type.

13. The method of claim 1 , wherein determining based on the comparison that the first type is compatible with the second type further comprises determining that the second type is a closed type preventing additional fields from being added to the second typed data structure and determining that the second typed data structure has no additional members beyond those defined in the first typed data structure.

14. The method of claim 1 , wherein determining based on the comparison that the first type is compatible with the second type comprises determining that the first type and the second type, which differ only in that the first typed data structure specifies a value of true for a nullability property while the second typed data structure specifies a value of false for a nullability property, are structurally compatible when the second type is nullable.

15. In a computing environment, a computer storage medium storing computer executable instructions that when executed by a processor cause the following acts to be performed:

accessing a first typed data structure defined in a mark-up object of a first type, the first typed data structure comprising a first plurality of fields, wherein each of the first plurality of fields defines a member of the first type consisting of one of a property, a method, or an event of the first type, wherein each member has a name and a type;

accessing a second typed data structure defined in a mark-up object of a second type, the second typed data structure comprising a second plurality of fields, wherein each of the second plurality of fields defines a member of the second type consisting of one of a property, a method, or an event of the second type, wherein each member has a name and a type;

comparing the first typed data structure to the second typed data structure to determine if the first and second types are compatible, wherein the comparison is performed by comparing the members of the first typed data structure to the members of the second typed data structure; and

determining based on the comparison that the first type is compatible with the second type if for each member in the first typed data structure, there is a member in the second typed data structure that has the same name and a compatible type.

16. The computer storage medium of claim 15 , wherein comparing the first typed data structure to the second typed data structure to determine if the first and second types are compatible further comprises:

determining that the first and second typed data structures each have the same values defining the nullability, identity and referenceability of their respective type.

17. The computer storage medium of claim 15 , wherein determining based on the comparison that the first type is compatible with the second type further comprises determining that the second type is a closed type preventing additional fields from being added to the second typed data structure and determining that the second typed data structure has no additional members beyond those defined in the first typed data structure.

18. The computer storage medium of claim 15 , wherein determining based on the comparison that the first type is compatible with the second type comprises determining that the first type and the second type, which differ only in that the first typed data structure specifies a value of true for a nullability property while the second typed data structure specifies a value of false for a nullability property, are structurally compatible when the second type is nullable.

19. The computer storage medium of claim 15 , wherein at least one of the first type or the second type is a description comprising an instantiation of a type.

20. The computer storage medium of claim 15 , wherein at least one of the first or second plurality of fields comprises a property identifying the first or second type as nullable by specifying a value may be represented by a null construct.