Abstract:
There is disclosed a method, apparatus and computer program for deriving overlay information from a user input for a base message schema associated with a node in a message flow. The base message schema is presented to the user and has at least one variable portion. A user selection of a variable portion of the base schema is received. The user is then provided with possible overlay schema information for the selected variable portion. A user selection of the schema to be overlaid on the selected variable portion is received. The selected overlay schema is associated with the base schema.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of European Patent Application No. 07150350.2 filed 21 Dec. 2007, entitled “A METHOD, APPARATUS AND COMPUTER PROGRAM FOR DERIVING OVERLAY INFORMATION FROM A USER INPUT FOR A BASE MESSAGE SCHEMA ASSOCIATED WITH A NODE IN A MESSAGE FLOW”, which is assigned to the assignee of the present application, and the teachings of which are hereby incorporated by reference in their entirety. 
     BACKGROUND 
     The invention relates to message processing and more particularly to the use of schema information in the processing of a message. 
     It is known for business applications to use web services, messaging etc. to communicate with one another over an Enterprise Service Bus (ESB). For example, a certain class of applications may send messages to each other using messaging systems, which are connected together via the bus. In this way, one application connected to one messaging system may talk to a different application connected to another messaging system. 
     Applications interacting across an ESB commonly use messages such as XML messages to communicate with one another. Messages are normally described by type definitions (schema) that define the message structure and allowable content. Message type definitions may include weakly-typed fields, where the actual message contents may vary and more than one definition may apply for that part of the message. For XML messages and in some other cases, XML Schema provides the type definition, and weakly-typed fields are most commonly encountered where the “any”, “anyType”, or “anySimpleType” constructs are used. These are constructs that are well known in the art. 
     Tasks such as viewing message structure, for example, in order to define transformations between one message type and another usually depend upon a visualization of the message structure, which is derived directly from the message type definition. Visualizing the content of weakly-typed fields is difficult, because their content structure is variable, and the XML Schema or other type information does not describe the content fully. In these situations, the result is an incomplete visualization of limited assistance for defining how these messages should be handled, and the end user must often write custom logic to handle the weakly-typed content. 
     SUMMARY 
     According to first aspect, there is provided a method for deriving overlay information from a user input for a base message schema associated with a node in a message flow. The method can present the base message schema to the user. The base message schema can have at least one variable portion. A user selection of a variable portion of the base schema can be received. The user can be provided with possible overlay schema information for the selected variable portion. A user selection of the schema to be overlaid on the selected variable portion; can be received. The selected overlay schema can be associated with the base schema. 
     In one embodiment, an overlay instruction can be generated that contains information for locating the selected variable portion. In one embodiment, the overlay schema can be associated with the overlay instruction. In one embodiment, a message structure can be visualized by providing an amalgamated view of the base message schema and any defined overlay schemas. In one embodiment, a second message structure is visualized and the two message structures can be used to define mappings between fields in both structures. In one embodiment, a connection between a first node in the message flow and a second node can be permitted based on one or more schema propagation rules. In one embodiment, the two nodes can have the same base schema associated therewith and the rules can assert that connection is acceptable if only the first node (and not the second node) has an overlay schema associated therewith. 
     According to a second aspect, an apparatus can be provided for deriving overlay information from a user input for a base message schema associated with a node in a message flow. The apparatus can include a means for presenting the base message schema to the user. The base message schema can have at least one variable portion. The apparatus can include a means for receiving a user selection of a variable portion of the base schema, a means for providing the user with possible overlay schema information for the selected variable portion, a means for receiving a user selection of the schema to be overlaid on the selected variable portion, and a means for associating the selected overlay schema with the base schema. 
     According to a third aspect, a computer program can be provided that includes a program code means adapted to perform the method of the first aspect when said program is run on a computer. The computer program can be stored in a storage medium, such as a volatile or non-volatile memory. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates a exemplary overview of the system of the present invention, in accordance with a preferred embodiment; 
         FIG. 2  illustrates the mediation component in more detail, in accordance with a preferred embodiment of the present invention; 
         FIGS. 3 and 5  show, in accordance with a preferred embodiment, the processing of the present invention; 
         FIG. 4  show, in accordance with a preferred embodiment of the present invention, the information associated with a set node; and 
         FIGS. 6 a  to 6 f    show, in accordance with a preferred embodiment of the present invention, how schema (type) information is propagated through a message work flow. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an overview of an exemplary Enterprise Service Bus. A bus  50  is provided to connect applications  20 ,  30  together. Such applications  20 ,  30  connect into the bus using Bus Connection Points (BCP). Various BCPs  15 ,  25 ,  35 ,  40  are provided for this reason. By way of example only, the BCPs may be messaging system (e.g. IBM® WebSphere® MQ) queues or web services endpoints. The bus itself may include mediation logic  60 . A mediation may be used to process a message that is travelling along the bus. For example, a mediation may transform and/or log a message. (IBM and WebSphere are trademarks of International Business Machines Corporation in the United States, other countries, or both.) 
       FIG. 2  illustrates, in accordance with an embodiment of the present invention, the mediation component  60  in more detail. Mediation component  60  comprises a set of nodes. In the figure, a receive node can be provided to receive a message. A filter node can also be provided to determine which type of processing a message should undergo. For example, messages on the bus may relate to local and European orders. A local order will be processed by branch  1  and this includes a set  1  node, a transform  1  node and a send  1  node. A European order will instead be processed by branch  2 . This comprises a set  2  node, a transform  2  node and a send  2  node. 
     Each node has input and output terminals (not illustrated). Each terminal has message schema information associated with it. An input terminal&#39;s schema information defines the format of messages received by the terminal&#39;s node, while an output terminal&#39;s schema information defines the format of messages sent by the terminal&#39;s node. 
     As discussed previously, such schema information may be weakly typed. In other words, a schema may not fully define the format of a message. Such a format may depend upon the processing route taken by a message. For example, a local order message may need to look different to a European order message. 
     In the example of  FIG. 2 , the input and output terminals of the receive node have message schema  80  associated with them. Message schema  80  indicates that messages received by the receive node will be order messages. They will contain an order type (string). This will indicate whether the order is a local order or a European order. Each order will have an integer order number and some order details. The order details can include the item (string), a shipping address (complex type) and a cost (complex type). It will be noticed that both the shipping address and the cost information may vary. For example, if the order is a local order, then the address may include number, street, town, county and postcode. However, for a European order, the address may be in a completely different format and will also include country information. With respect to the cost field, a local order will be in a local currency such as GBP or USD, while a European order will use Euros. 
     The nodes in a mediation constitute a message flow which a user designs visually on a blank canvas. When a flow is first created, its input and output nodes (e.g. receive and send nodes of  FIG. 2 ) are provided and the terminals of these nodes carry type (schema) information. Such information is taken from interfaces and references defined on the mediation component.  FIG. 6 a    shows input node  300  and output nodes  320 ,  330 . Terminals are denoted by smaller square boxes (e.g.  310 ). In the figure, terminal types are marked A, B and C for simplicity. These signify the type of message expected to flow down associated branches of the flow. 
     As shown in  FIG. 6 b   , when a new node (Filter node) is dropped onto the canvas, its terminals are initially untyped. For explanatory purposes, these are marked with a *. 
     In  FIG. 6 c   , the input and filter nodes are wired together. As wiring is added, the terminal type information propagates down the wires, ‘filling in’ the untyped terminals. For nodes that do not change the message type, terminal typing information propagates across them, as with the Filter node shown in  FIG. 6 c   . Here, its terminals all acquire type A from the input node. 
     As shown in  FIG. 6 d   , for nodes that change the message type, schema information does not propagate across them. Thus, the input terminal for the transform node receives type A information but this is not propagated to its output terminal. This remains untyped (*), even when its input terminal is wired up. 
     Propagation also works in the reverse direction. When the output of the transform node is wired to the output node, the transform nodes output terminal receives type information from the output nodes output terminal. This is shown in  FIG. 6   e.    
       FIG. 6 f    completes the picture, with typing information propagating from the filter node to the transform  2  node and from the output  2  node to the transform  2  node. 
     In this way type or schema information propagates through a message workflow. To clarify, if two transform nodes (or other nodes which change the type information) are placed in succession, then the type is known based on the configuration of those nodes. For example, once a transformation has been configured, then the input and output message types are known. 
     As previously mentioned, schema information may contain portions which vary dependent upon the specific type of message. A new type of node, the SET node, is defined which allows a user to manipulate variable schema information. This is discussed with reference to  FIGS. 2 and 3 . A set node instance is created at step  100  and is wired into the message flow at step  110 . As shown in  FIG. 2 , a set node is wired in between the filter node and a transform  1  node. 
     At step  120 , the input terminal of the set node instance receives schema information from the previous node in the message flow. This is as discussed above. It should be clarified however that the schema information is preferably not actually sent between terminals but rather a pointer enabling access to such information. This provides for a more robust solution as will be explained later on. Thus at step  120  a pointer to the base message schema is received. 
     At step  130 , the user is presented with a graphical view of the base schema. Mechanisms for achieving this are already known in the art and so will not be discussed in any detail below. 
     Such a base schema may include variable portions as discussed above. The user is permitted to select a variable portion in order to overlay that portion with specific schema definition information. The mediation component stores possible schema (type) definitions from which the user may select and presents these at step  150 . At step  160 , the mediation component receives the user&#39;s type definition selection. At step  165 , an overlay instruction is generated which indicates which element within the base schema is to be overlaid. At step  170 , a pointer is provided to the selected type definition which is to be used as the overlay. Processing loops round for all variable portions within the base schema. 
       FIG. 4  illustrates the pointers that are thereby associated with a set node&#39;s ( 180 ) output terminal. The set node has a base id (Bid) pointer which points to the base schema in local storage. In this instance, the base schema  195  provides the base information that defines all message orders received by the mediation component. 
     The set node  180 , also has an overlay id (Oid) associated with it. This points to an instruction  185  in storage which provides an instruction for locating the element (variable portion) within the base schema that is to be overlaid and the instruction for overlaying this portion. Note that the element may be located using an XPath expression. 
     The overlay instruction in turn points to the information  190  that is to be overlaid. In this instance the order is a European order and so the address information includes country information. 
     Thus, the output terminal of the set node now has all the information necessary to more specifically define messages received. Such type information is propagated along the message flow as previously discussed. The propagation is a ‘tooling-time’ propagation. The tooling needs to be told precisely what to expect at a certain point in the flow so that when the message representation is shown it has the correct form. 
     Whether base and overlay schema information is permitted to be propagated is defined by some validation rules. When wiring two terminals together (connecting an arc between them) that do not have the same type map (i.e. they have a type mapping of their own, either because they are part of a dataflow node that asserts a type mapping or because they are connected to a dataflow node that asserts a type mapping), connection is either allowed or disallowed according to the following rules;
         1. An arc can be connected from an output terminal with base and overlay schemas (a strong type definition) to an input terminal with only a base schema (weak type definition); i.e. an input terminal with only a base schema can accept input from an output terminal with additional overlay information (because it is guaranteed that the message will conform to the base schema if it already conforms to the stronger type definition). It should be appreciated that both the base schemas should be the same.   2. An arc cannot be connected from an output terminal with a weaker type definition to an input terminal with a stronger type definition. This is because a weakly typed output terminal may produce an output that does not conform to the specific stronger type.       

     Having more strongly defined the schema (type) information, it is now possible to use such information to visualize the contents of a message or to define the mappings required when transforming between two message types. 
     When visualizing a message, the current node&#39;s input terminal&#39;s message schema is typically used to render the message appropriately. (For a mapping (transformation) visualization is performed of both input and output message structures, based upon the input and output terminal information respectively.) This is discussed in more detail with reference to  FIG. 5 . At step  200 , a message structure is selected on which to perform visualization. At step  210 , the base schema is accessed using the Bid pointer. At step  220 , the overlay instruction(s) defined for the base schema at this particular node is accessed using the Oid pointer. The overlay information subsequently pointed to is then accessed at step  230 . Finally, at step  240  the selected message structure is displayed using the amalgamated schema information. 
     The base schema, overlay instruction and overlay information are however stored separately as discussed and do not need to be amalgamated even when the internal structure of the base or overlay type is modified. That is, although what looks like an amalgamated view of the overall message structure is produced, that view will automatically reflect any changes made to its constituent parts. 
     It should be appreciated that a new schema is not actually created. Rather, the message in accordance with a virtual view of an underlying message schema is presented. This provides for a much more robust solution since the parts of the schema can be individually edited. If a new schema was actually created, then it would not be possible to edit the constituent parts without the overall schema becoming out of date. 
     It should further be appreciated that it is optionally possible to validate messages at runtime to determine whether they conform to the amalgamated ‘virtual view’ of the underlying schema. For validation it is the input schema that is used.