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2009-02-13 Heinemann questions 2.3 (page 62)

posted Feb 12, 2009, 3:37 PM by Unknown user   [ updated Apr 10, 2009, 2:07 AM by Eddie Woo ]
For further details, please refer to IPT: Overview of Databases
  1. The database is the data/information that is processed by the DBMS (database management system). Comparing a database to a DBMS is similar to comparing a text file to a text editor.
  2. An index is a table that contains information about the location of data. It is a "map" with which the system can find the data.
  3. A distributed database is one which is collectively one database, but one where parts of the database are located in different places geographically. The internet is one very, very large distributed database - it is one collective thing (the "web"), but bits and pieces of it are located everywhere around the world, hence "world wide web".
  4. Information systems use three types of storage - local, network, and portable. Local storage is connected directly to the informaion system, network storage is accessed by the information system through a network connection, and portable storage is easy to move around.
  5. Public key encryption is a method of encrypting data, requiring the sender to provide the recipient with the "key" - a password with which the encrypted data can be decrypted.
  6. Backup and recovery is a method of securing data, by making a "backup" - an identical copy of the data that is stored separate from the information system. The data in the backup can be put back into active use by returning it to the information system - this process is known as "recovery".
  7. Searching is to look for something. Sorting is to place items in a logical order.
  8. QBE is a three letter acronym for "Query by example", a query language for relational databases developed by an IBM employee with the name, "Moshé M. Zloof". Some fields are filled in, and these filled-in fields are considered criteria for a full search of the database.
  9. SELECT: "Choose this field..."; FROM: "...from this table."; WHERE: "Give me everything that fits this criteria..."; ORDER BY: "... and arrange them in this way"
  10. A search engine regularly sends out "spiders" to "crawl" the "web". These "spiders" have the sole purpose of thoroughly exploring the web, and report back to the search engine with any new discoveries, as well as changes to existing websites. This data is then added to the database of websites.
  11. A search engine with directories classifies every website it finds. This is similar to the DET filtering system, and like the DET filtering system, the added task of classifying every website means that a lot of useful websites remain "uncategorised". As a further parallel to the DET filtering system, these "uncategorised" websites are unaccessible through the search engine.
  12. A search "robot" has the sole purpose of thoroughly exploring the web, and reporting back to the search engine with any new discoveries, as well as changes to existing websites. This data is then added to the database of websites.
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