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2009-10-20 Questions and Answers

posted Oct 19, 2009, 11:35 PM by Unknown user   [ updated Oct 20, 2009, 9:21 PM by Eddie Woo ]
I asked Mr. Woo some questions about the course today (in the morning class and then in period 1). Here are the answers (as I remember them), because:
  • I find that I absorb new stuff easier if I have to describe them;
  • I need some practise with HSC keywords;
  • Some of you other 10IPT'ers might find this useful, and we want to come first, right? :D
If you find anything wrong with what I have typed here, please let me know. We're all in this together.

1. Identify the purpose of packet switching, and explain how packet switching works. (Communications)

Packet switching exists to allow a message to be transmitted in a more efficient way in a network where there are multiple possible routes from the sender to the recipient. It works by splitting a data transmission into groups of bytes called packets. The sizes of these packets are determined by protocol (e.g. 4 bytes per packet). These packets are sent simultaneously, each on a separate route to the recipient. They will arrive in an arbitrary (random) order, but can be utilised by the recipient in the correct order by identification features in the packets.

2. Clarify the possible meanings of the terms "relationship", "entity", and "attribute". Propose the most suitable term to refer to things they represent (in a HSC exam), and justify your response. (Databases)

Much like how the term friendship refers to the way in which two friends are connected, a relationship describes the way in which one table in a relational database is linked to another one. They are the links between tables, and can be one-to-many, many-to-one, one-to-one, or many-to-many, as described by the Board of Studies IPT syllabus. While the definition given by the Jacaranda1 textbook ("a relationship is a table or file created by joining together data from different databases") can be considered valid in an abstract way (in that a relationship is required for two tables to share data), it appears to be conventional to refer to relationships as the links between tables, and not the tables2 involved.

An entity is a specific tangible person, place, or thing. Databases store data about entities, such as students in classrooms, classrooms in schools, cities in states, states in countries, products sold by a department store, etc. The Heinemann3 textbook implies that an entity could also be the name given to a table that contains data about a specific type of entity (e.g. a table about students could be termed the "Students entity"), a notion that is supported by the syllabus' intepretation of tables as "implementations of entities". It appears that this convention is occasionally followed by the Board of Studies4.

An attribute describes a known feature of entities about which a relational database stores data. This notion is supported by both the Heinemann3 textbook ("attributes are the same as fields in a flat file database") and Wikipedia2; however, the Jacaranda1 textbook proposes that "an attribute is a field copied from a parent database", implying that a field in a relational database is only an attribute if it contains data from another table. Nevertheless, the Jacaranda textbook adds that "attributes are the columns in a relationship table shown in list view", which is implicit of support to the definition of an attribute as being any field in a table in a relational database.

In a HSC exam, it is most suitable to refer to tables as tables, links as links (or relationships if the questions is about one-to-one, one-to-many, many-to-one, or many-to-many relationships), and fields as fields, due to the ambiguity from different textbooks. Referring to fields with data from other tables as attributes, however, is ideal, as no definition of attributes presented by any of the textbooks would contradict this.

3. Propose which network topologies can utilise collision detection, and justify your response.

All major network topologies (star, bus, ring, point-to-point, hierarchical, and mesh) can use collision detection, because collisions will still occur regardless of efforts to minimise their abundancy (e.g. protocols such as token rings in ring networks). However, as collisions are significantly more common on bus networks, it is bus networks that use them the most.

4. Describe intelligent agents.

Intelligent agents are decision support systems that make decisions and implement the best decision in each case autonomously, rather than proposing an array of possible decisions to the end user. An example of an intelligent agent is a search engine that displays what it believes to be the most relevant result. Intelligent agents are still a form of decision support because humans ultimately still have the power to prevent the intelligent agent from implementing decisions.

Some miscellany:
  • When questions in Decision Support Systems part of Section III talk about "neural networks", e.g. "describe how a neural network works", they are always talking about artificial neural networks.
  • If there are a bunch of computers pointing to and from a circle at the center of a network, do not assume that the circle represents the central server of a star network - it may be representing the ring of a ring network or, indeed, the network itself
  • A primary key is a key field; a foreign key is a primary key when it's an attribute in another table
  • Normalise databases by drawing a schema
  • "Mobile technology" refers to mobile phones
  • Certainty factor (CF) is only for probability
  • If a question asks you to draw relationships between items, don't talk about items in isolation
  • A byte can store:
    • One ASCII character
    • Any number from 0 to 255
  • Try to answer S&E issues questions from differing perspectives in terms of people and groups of people
  • Date is stored as the "date" data type (thank you Jason and Komal)
  • Decision tree going down a page is fine

1 Information Processes and Technology: HSC Course (Ware, Cheleski & Chivers, 2001), page 48
2 Wikipedia proposes that these tables should be called relations, not relationships
3 Information Processes and Technology: HSC Course (G. K. Powers, 2000), page 44
4 A database schema is said to consist of "relationships, entities and attributes" according to the answers to question 4 of the 2001 Board of Studies paper; this same idea is presented by the syllabus