ISSUE 66: Proposed Resolution, Second Attempt

["Barack, Ron" <ron.barack@sap.com>]

Title: 4

Hi Everyone,

I've tightened up the definition of compatibility. Although it doesn't go so far as to say "exactly the same except...", I think most of the problem cases are avoided, while still support our SCA wiring use-cases. I'd be pretty sorry to make supporting compatibility between types that have different containment structures a vendor extension: it's just too important to our JPA/DAS -> BPEL use case.

If this wording is not acceptable, let's try to do a couple of iterations over the mailing list.

Best Regards,
Ron

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4.5.2    Type Contents

A Type will always have:

• Name - A String that must be unique among the Types that belong to the same URI in the same HelperContext.
• URI - The logical URI of a package or a target namespace, depending upon your perspective.
• Boolean fields indicating if the type is open, abstract, sequenced, or a data type.

 

A Type can have:

• Properties - a list of Property objects defined by this Type. Types corresponding to simple data types define no properties.
• Instance Class - the java.lang.Class used to implement the SDO Type.
• If DataType is true then a Type must have an Instance Class. Example classes are: java.lang.Integer and java.lang.String.
• If DataType is false, and generated code is used, then an Instance Class is optional. Examples classes might be: PurchaseOrder and Customer.

·       Aliases - Strings containing additional names. Alias Names must be unique within a URI. All methods that operate on a Type by name also accept alias names. For example, a Type might be assigned an alias name for the domains it is used in: an XML Schema name "PurchaseOrderType", a Java name "PurchaseOrder" and a database table name "PRCHORDR". 

·       Instance properties – open content metadata extensions attached to the Type instance.

 

4.5.3    Name Uniqueness

Within a single HelperContext, the combination of a URI and a Type names or Type alias names uniquely identifies the type. Other HelperContexts may have different (and conflicting) definitions for types having the same URI and name.

Property names and Property alias names are all unique within a Type and any base Types.

4.5.4    Compatibility Between Types

Types in different HelperContexts may represent the same underlying business data.  Often Types in different contexts are closely enough related that it is possible to transfer the business data between the contexts using the DataHelper.project() method.  Types that are closely enough related to allow this are termed compatible Types. 

The following rules are used to determine compatibility.

1. Two DataTypes are compatible if they have the same instance class.
2. A complex type T1 is compliant with a type T2.  The types are compliant if 

a)     The URI and name of both types are equal.

b)     Both types are concrete.

c)     T1.isSequenced() is identical to T2.isSequenced()

d)     T1.isOpen() is identical to T2.isOpen()

e)     T1.isNullable() is identical to T2.isNullable()

f)       For every property P1 in T1 there is a property P2 in T2 such that

                                                    i.     P1.getName() is equal to P2.getName()

                                                   ii.     P1.getType() is compatible with P2.getType()

                                                  iii.     P1.isMany() is identical to P2.isMany()

                                                  iv.     XMLHelper.isXmlElement(P1) is identical to XMLHelper.isXmlElement(P2)

g)     For every property P2 in T2, there is a property P1 in T1 such that

                                                    i.     P1.getName() is equal to P2.getName()

                                                   ii.     P1.getType() is compatible with P2.getType()

                                                  iii.     P1.isMany() is identical to P2.isMany()

                                                  iv.     XMLHelper.isXmlElement(P1) is identical to XMLHelper.isXmlElement(P2)

 

 Implementations may choose to loosen these requirements on compatibility, for instance, an implementation may choose to allow the set of properties in T1 to be a subset of the properties in T2, that is, to require either 2.f or 2.g.  An implementation definition of compatibility may not be made more restrictive.  In particular, the following characteristics may not be used in determining if types are compatible

1. The instance class (that is, the static SDO) associated with a complex type.
2. Whether the value of P1.isContainment() is identical to the value of P2.getContainment()
3. The XML or Java names of the properties.
4. Any validation information (e.g., XSD facets) associated with a DataType
5. The order of the properties in Type.getProperties()
6. The base types associated with either of the types.
7. Whether or not properties are defined as bi-directional.

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4.14.2          The Project method

The DataHelper.project() method is used to move data between contexts.  The behavior of this method is as follows.

Consider object O1, where O1.getType() is T1 and where T1.getHelperContext() is C1.  Consider a context C2 that defines a Type, T2, that is compatible to T1 according to the definition in section 4.5.4.  The method

     DataObject O2 = C2.getDataHelper().project(O1);

returns a DataObject O2 such that  

1.      O2.getType() is T2

2.      If P1.getType().isDataType() is true then O1.get(P1)==O2.get(P2)

3.      If P1.getType().isDataType() is false, then if O1.get(P1) is null, O2.get(P2) is null, otherwise

    O2.get(P2)==C2.project(O1.get(P1))

If O1 and O2 are both sequenced, then the order of the elements in the sequences will match.

If C2 does not define a type that is compatible to T1 according to the definition in section 4.5.4, the project operation MUST throw an exception.

The project operation leaves the DataObject O1, and all objects in the transitive closure reachable from O1  in an undefined state.  O1 may be returned to a defined state by reversing the project operation, i.e.,

     C1.getDataHelper().project(O2);

Notice that each DataObject has a single representation in each context,  That is,

     DataObject O2 = C2.getDataHelper().project(O1);

     DataObject O3 = C2.getDataHelper().project(O1);

     assertSame(O2, O3);

     DataObject O4 = C1.getDataHelper().project(O2);

     assertSame(O1, O4);   

 

The project method must assure that the object returned from a projection is valid according to the rules defined in the context where the object’s type is defined.  This includes restrictions derived from the type’s containment structure, e.g., there can be no objects in the containment graph reachable from the projected object that have more than one container.  For instance, consider an object P1, with Type T1, in context C1.  Assume that it has 2 properties, “a” and “b”, neither of which are marked as being a containment property.  Then it could be legal to set the value of these properties to the same object, N1.   Now consider a second type, T2, in context C2, that is compatible with T1 but in which the properties “a” and “b” are both marked as being containment properties.  Then the DataObject P1 cannot be projected into the context C2, because the object N1 would project to an object that has conflicting containment properties.

Similarly, an implementation must check than any bi-directional properties have consistent values.  Of course, this is automatic if the properties are bi-directional in both HelperContexts.  In the case where the original object does not have a bi-directional property, an implementation must check the consistency of both side of the property.

If the project operation would result in a datagraph that violates the restrictions imposed by the type definitions in that context, the project method MUST throw an exception.