Slide 15 of 52
Notes:
There are two sorts of transactions involved in any engineering data system, whether it is GIS, CAD or anything else:
- short transactions: a single value is changed and the result confirmed as committed to the repository (database or filesystem).
- long transactions: a substantial segment of the data is 'checked out' by an engineer for several days or weeks work, during which time that data is in an inconsistent state. When completed and consistent, it is 'checked in' to the database again. Meanwhile, read-only users see only the previous, consistent view of the data.
Although there are no fundamental reasons why it should be the case, it is nevertheless a fact that OO GIS vendors have found it very much easier to offer long-transaction support than have RDBMS vendors, e.g. ESRI plan to announce long transactions in Winter 1998 whereas Laser-Scan and Smallworld have provided them since the early-mid 1990s.
