312 CHAPTER 10 INFINITE DATA PATTERN In the XML, the element TransactionIdentifier has an associated value of 1, and the XML element Number has an associated value of 20. When a result structure is generated, the XML will appear similar to the following: success 1 9 The main difference between the XML to be sent and received is the additional XML element Result to indicate a success. The Result element is necessary so that the client knows what to do with the XML content. For example, imagine sending a state that has incorrect data. The error condition is not generated on the sending of the data, but on the receiving of the data. This is due to the requirement of the Persistent Communications pattern and asynchronous communications. To indicate that an error has occurred, a result has to be sent with the error. Another reason for using the Result element is to indicate a finished operation, indicating that all results have been found and that the client will not receive any more results. There is one weakness with using simple transaction identifiers 1and 2: if a user sends an Action XML document with transaction identifier 1, and then shortly thereafter sends another Action XML document with the same transaction identifier, the results will be corrupted. The results are corrupted because two tasks would generate data using the same transaction identifier even though the state for each transaction identifier may be different. The solution is to create a unique transaction identifier for each and every sending of structured data that generates results. The following modified Action XML document references the corrected transaction identifier: 1_1 20 In the modified XML, the transaction identifier has encoding so that the first digit represents the first or second result field, and the second digit is the transaction identifier counter. The encoding of the transaction identifier seems arbitrary, and is arbitrary from the perspective of the server because only the client knows how to decipher the identifier. The server, when presented with the transaction identifier, does not attempt to decipher what the identifier means. The server is responsible only for cross-referencing the transaction identifier with the received and result data. Generating the Content for the Contract Having defined the contract between the client and server, the next step is to generate the content for the contract. The JavaScript code used to generate the state will be illustrated first, and then the code used to process the received results. For this explanation, it is assumed that the server sends and receives the data without any errors or problems. The data sent from the client to the server is created in either the function SendData1 or SendData2. For explanation purposes, the implementation of SendData1 is outlined. It is not necessary to explain SendData2 because it is nearly identical to SendData1. The main difference
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