Chapter 2 • Synchronizing at a Glance

Time Stamp, Identity Mappings, and Record Versions

The Synchronizer stores various data during the synchronization process. During subsequent synchronization runs, the Synchronizer uses this data to determine if a record needs to be synchronized. The stored data includes:

➤Time stamp. Indicates when the last synchronization task started running on a specific link.

➤Identity mappings. For each link, the Synchronizer stores a table of identity mappings between records in each endpoint. Each record in each endpoint is identified by a unique ID, and this table records the correspondence between each pair of records.

➤Record versions. Indicates the version of each synchronized record in each endpoint. During synchronization, each synchronized record receives a unique version.

Cycle Redundancy Checks

After the Synchronizer has determined that a mapping is a candidate for synchronization, a cycle redundancy check (CRC) is performed to determine whether to synchronize the records in the mapping. A cycle redundancy check is a mathematical operation used to indicate whether data in an endpoint has changed.

The Synchronizer performs a cycle redundancy check for each endpoint on the mapped fields only. This enables the Synchronizer to determine whether the modifications made to the records in the mapping necessitate synchronizing the records.

For example, suppose you are mapping defects in Quality Center with defects in ClearQuest, and the only field mapping for the link is between the Status field in Quality Center and the State field in ClearQuest. Suppose the Priority field is updated for a defect in Quality Center. As the defect was modified, the mapping that includes the defect is a candidate for synchronization, based on the link time stamp. However, as the mapped fields were not modified, the records should not be synchronized, even though there were other modifications to the records. During synchronization, the Synchronizer performs a cycle redundancy check on the mapping. The check indicates that the mapped fields were not modified, and therefore the records are not synchronized.

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