Learning Algorithms Web Service Composition - CodeShoppy
Learning Algorithms Web Service Composition - CodeShoppy
Timestamps can be applied to records in order to recordthe time when a record has been inserted or updated. It isnot possible to capture record deletions with timestamps,because the timestamps get deleted with the record. Times-tamps take relatively little time to set up, and they aremaintained by the DBMS. Figure 3 shows the timestampsapproach to CDC. Change data will be timestamped whenthe DBMS records it. The CDC tool will poll the database,and look for records that have been added or modified sincethe last scan. The timestamps should be indexed in orderto improve the performance of the CDC tool.
One of the goals of real-time CDC is to propagate thechanges through the system without interruption. Moreover,an ideal CDC system will automatically allow changes toflow from the source system to interested target systems. Toattain this flow, it is imperative that the CDC tool knowswhere to deliver the changed data to. One way of doing thisis to hard code the target destinations into the CDC tool. Amore flexible system will freely allow targets to be addedand removed when required.
Obviously there can be multiple target destinations forthe changed data, and it is likely that each destination willrequire different changed data. An intelligent CDC systemwill know what data to deliver to each of the interested targetsystems. This feature is seldom implemented.Therefore, we propose a framework for a CDC systembased on web service technology. Our framework willprovide the foundation for a CDC architecture that canautomatically allow targets to subscribe to changes and alsoallow the changes to be filtered to tailor each targets datarequirements.
The framework shown in Figure 4 depicts how publishersand subscribers interact within our framework. The pub-lisher is a web service with two operations,Subscribe()andNotify(). Interested targets will consume the Publisherweb service and register by callingSubscribe(), passing inan XQuery as the parameter. When changes arrive at the publisher, theNotify()operation will automatically send thedata to the targets, applying the XQuery to the changed data,therefore filtering the data, so that the target subscriber getsonly the changed data .
