Locking a Recordset
We need to keep track of whether the data on the central data source has changed since we made our copy. This is the job of one of the arrays inside the cRecordset, known affectionately as the CRUD array.
The CRUD array indicates whether this row has been Created, Updated, Deleted, or just plain old Read. Also stored is a globally unique identifier (GUID) for this particular row. This unique identifier must be automatically updated when a row is modified on the data source. These two parameters are used by the DAL in the UpdateRecordset method to determine whether a row needs updating and whether this row has been modified by someone since the client received the recordset. This process is a form of software locking, although it could be internally implemented just as easily using timestamps (if a given data source supports them).