# Questions and Answers on Union and Intersection

Topics: Binary numeral system, Logic, Computer Pages: 3 (885 words) Published: March 21, 2013
Primary Task Response: Write at least 3 paragraphs that respond to the following questions with your thoughts, ideas, and comments. Be substantive and clear, and use examples to reinforce your ideas. Part I: Describe how the notion of union and intersection apply to retrieving records in databases. Give an example of 2 sets that might appear in a database to help in your description. A prominent couple is found murdered in their mansion located in an affluent neighborhood. The housekeeper found the bodies and called the police. The housekeeper tells the detectives that quite a few valuables are missing from the house: artwork, electronics, jewelry, cash etc.

In the initial stages of the investigation the detectives cannot decide whether this was a robbery gone wrong or a murder the perpetrator tried to disguise into a robbery. Not wanting to miss any potential leads the police compiles a joint list of suspects: every suspect on this list is either a known robber or a known killer (or both).

For the first set R={x| x has a robbery rap sheet} they access the Theft/Robbery Division database. For the second set M={y |y has a murder in his criminal record} they access the Homicide Division database.

It is not uncommon that different divisions within the same police department maintain different databases. Although state and national databases do exist they are usually slow moving and most often than not they generate unmanageably long lists of suspects. The advantage of a local database consists in a much easier access and output which is oftentimes much more relevant to the investigation – in 99% of the cases the crime is perpetrated by a local suspect.

Thus the initial set of suspects S is the union of R and M: S=R∪M. Suppose however that S has too many suspects. Given the personnel shortage it is not feasible to investigate every name which appears in S. the police needs to find a way to narrow down this list. After re-interviewing the neighbors, it...

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