We are nearly ready to discuss the penultimate pattern, Version Pattern 6. This pattern expresses the combined semantics of all the version patterns we have discussed so far. The last versioning requirement we will examine adds the requirement to version error corrections, and it is Version Pattern 7 that will accommodate that requirement, as well as all the patterns previous to it. Version Pattern 7 is therefore the “ultimate” versioning pattern to be discussed in these articles. It is clear that if Pattern 6 can express the semantics of patterns 4 and 5, it can express the semantics of all prior patterns. And indeed it can. Like Pattern 4, it distinguishes business effectivity dates from database activity dates, making it possible, for example, to create new versions in advance of the date on which they will become effective. Like Pattern 5, it manages versions which may have temporal gaps between them, making it possible, for example, to record the reappearance of an object after its absence for some period of time. But before we discuss Pattern 6, there are two preliminary matters to address. The first is to provide a roadmap to the rest of the articles in this series. The second is to introduce the use of a special set of surrogate keys for versioned tables, and explain why they are needed and how they will be used. The rest of this article lays out that roadmap. Then, Parts 14 & 15 make the case for using surrogate keys, and describes the special considerations needed to make surrogate keys work with versioned tables. Chart of Version Patterns Before continuing, we insert here the current chart of version patterns. References back to earlier patterns are happening pretty frequently now, and we hope this will help the reader recall what those prior version patterns are. They also give a hint of version patterns not yet discussed. Figure 1: Chart of Version Patterns Chart of This Series Before continuing, we insert here a chart listing the installments to date in this series, and a brief description of what each one is about. As this series grows longer, the back references to earlier installments will only increase, and we think that having a chart like this at hand will be helpful. Figure 2: Chart of Installments to Date in this Series
Roadmap for the Remainder of the Series
The high-level view of the roadmap to the rest of this series is as follows. Items are listed in the sequence in which they will be discussed.
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Versioning with surrogate keys.
