Lesson plan
Recursive join
The recursive join is an operation used in relational databases, also sometimes called a "fixed-point join". It is a compound operation that involves repeating the join operation, typically accumulating more records each time, until a repetition makes no change to the results (as compared to the results of the previous iteration). For example, if a database of family relationships is to be searched, and the record for each person has "mother" and "father" fields, a recursive join would be one way to retrieve all of a person's known ancestors: first the person's direct parents' records would be retrieved, then the parents' information would be used to retrieve the grandparents' records, and so on until no new records are being found. In this example, as in many real cases, the repetition involves only a single database table, and so is more specifically a "recursive self-join". Recursive joins can be very time-consuming unless optimized through indexing, the addition of extra key fields, or other techniques. Graph traversals come at a lower cost than the method of recursive joins. Recursive joins are highly characteristic of hierarchical data, and therefore become a serious issue with XML data.…
Article summary
The recursive join is an operation used in relational databases, also sometimes called a "fixed-point join". It is a compound operation that involves repeating the join operation, typically accumulating more records each time, until a repetition makes no change to the results (as compared to the results of the previous iteration). For example, if a database of family relationships is to be searched, and the record for each person has "mother" and "father" fields, a recursive join would be one way to retrieve all of a person's known ancestors: first the person's direct parents' records would be retrieved, then the parents' information would be used to retrieve the grandparents' records, and so on until no new records are being found. In this example, as in many real cases, the repetition involves only a single database table, and so is more specifically a "recursive self-join". Recursive joins can be very time-consuming unless optimized through indexing, the addition of extra key fields, or other techniques. Graph traversals come at a lower cost than the method of recursive joins. Recursive joins are highly characteristic of hierarchical data, and therefore become a serious issue with XML data.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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