VCE IT Helpdesk

[excal]

 :knuppel2:

(for many to many, you will need a linking table - has someone taught you this?)

hell no, stupid teacher didn't teach my class shit.

Ok, I'll try my best to explain what a linking table is in this medium (it's quite a difficult concept to grasp without face to face interaction).

Consider three students - 'A', 'B' and 'C'
and two classes - 'ENG' and 'METHODS'

A student can be enrolled in one or both classes, and both classes can have as many students as they want.

This would imply two tables, a 'STUDENT' table and a 'CLASS' table, which would contain the information above:

Code: [Select]


mysql> SELECT * FROM student;

+------------+------------------+
| STUDENT_CD | STUDENT_NAME     |
+------------+------------------+
| A          | ABA JONES        |
| B          | BOB THE BUILDER  |
| C          | CHARLIE BROWN    |
+------------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM class;

+--------------+----------------------+
| CLASS_CD     | CLASS_NAME           |
+--------------+----------------------+
| ENG          | ENGLISH              |
| METHODS      | MATHEMATICAL METHODS |
+--------------+----------------------+
2 rows in set (0.00 sec)

mysql>

Now, consider how you would implement the fact that a) a student can have many classes and b) a class can have many students. Note that we do not know *exactly* how many people a class will have with certainty, so that rules out adding extra fields (studentA, studentB ...studentn) and making it a foreign key. The same is true for the reverse.

This is also bad normalisation (well-forming a database) practice.

Nor can we have a class foreign key in the Student table and have multiple Student records the more classes they are in as this would violate the primary key's uniqueness.

If we set both the Class foreign key in the Student table AND the Student's ID as a composite primary key, this will work (and vice versa). However we will run the risk of what are known as data redundancy errors. Take this for example:

Suppose student A were enrolled in both ENG and METHODS. We have added a composite primary key field to the Student table 'Class_cd' which is also a foreign key to the Class table. The table should now look like this:

Code: [Select]

mysql> SELECT * FROM student WHERE student_cd = 'A';

+------------+------------------+--------------+
| STUDENT_CD | STUDENT_NAME     | CLASS_CD     |
+------------+------------------+--------------+
| A          | ABA JONES        | ENG          |
| A          | ABA JONES        | METHODS      |
+------------+------------------+--------------+
2 rows in set (0.00 sec)

mysql>

I now want to change student A's name as they've become married. While doing a blanket 'change name to 'ABA RODGERS' against all student As, we run the risk of a program or database user inadvertently changing just the one. Now we have inconsistent data.

The 'best practice' solution is similar to the above, but to create a NEW table to achieve it. This is known as the linking table. This is simply a table that has foreign keys from Class and Student, but both combine to be a composite primary key (to ensure uniqueness between each 'instance' of a Student's participation in a Class).

Going back to the tables as they were before:

Code: [Select]


mysql> SELECT * FROM student;

+------------+------------------+
| STUDENT_CD | STUDENT_NAME     |
+------------+------------------+
| A          | ABA JONES        |
| B          | BOB THE BUILDER  |
| C          | CHARLIE BROWN    |
+------------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM class;

+--------------+----------------------+
| CLASS_CD     | CLASS_NAME           |
+--------------+----------------------+
| ENG          | ENGLISH              |
| METHODS      | MATHEMATICAL METHODS |
+--------------+----------------------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM class_instance;

+------------+--------------+
| STUDENT_CD | CLASS_CD     |
+------------+--------------+
| A          | ENG          |
| A          | METHODS      |
+------------+--------------+


Relationship:



The use of the linking table will allow the database to remain consistent whilst expressing the fact that a Student may have many classes, and a Class may have many Students. The data (as in, if you wanted to retrieve the class listing with proper student details) can be re-retrieved by using a concept known as 'joins'. The Student table can be joined onto the Class_Instance table where Class_Cd = 'ENG', for example.

[jsimmo]

Do we need to know all the network topologies (star, bus, hybrid, tree)? Ofcourse they are easy to remember.. but I just wasn't sure if it falls under any heading within the study design?

[ell]

Do we need to know all the network topologies (star, bus, hybrid, tree)? Ofcourse they are easy to remember.. but I just wasn't sure if it falls under any heading within the study design?

From the ITA study design:

•  an overview of types and characteristics of networks, and functions of network operating systems;
•  suitability of types of transmission media to support local and remote communication, including cabling and wireless links;

These are the only two network-related dot points in the whole study design, but yes I would say that this implies you should know about the different topologies.

Interestingly, the Software study design explicitly mentions topologies:

•  types of networks, and strengths and weaknesses of different network topologies

But I'd make sure you knew enough about the different network topologies anyway, like you said they're not that difficult to learn.

[excal]

I suspect you only need to know topologies at a descriptive level and not describe benefits/cons of them.

That said, you need to know about network technologies.

For example, what is the best media for connecting two stations that are 200 metres apart where cost is a consideration?

[transgression]

I have a question

Are phone numbers and mobile number TEXT or NUMERIC?
I've done past exam papers, and get so confused when I read the answers.
They are TEXT because they cannot be added up as sums, but some papers refer to them as NUMERIC. I think we should stick with TEXT though. What about everyone else?

[Glockmeister]

phone numbers should be text as they can have () for area codes.

Also with numeric, it means they are number and thus we could do some statstical work on the data in the records. Don't think we want to do that with a mobile number.

[excal]

What Glockmeister said.

The validation of a phone number can be achieved in Access by use of an input mask. It will, however, be of a 'Text' type.

I'd also extend what Glockmeister said to any work to do with reporting, not just stats.

[jsimmo]

Does anyone have a solid definition for:

- lag/slack time
-task dependencies

[RD]

:knuppel2:

(for many to many, you will need a linking table - has someone taught you this?)

hell no, stupid teacher didn't teach my class shit.

Ok, I'll try my best to explain what a linking table is in this medium (it's quite a difficult concept to grasp without face to face interaction).

Consider three students - 'A', 'B' and 'C'
and two classes - 'ENG' and 'METHODS'

A student can be enrolled in one or both classes, and both classes can have as many students as they want.

This would imply two tables, a 'STUDENT' table and a 'CLASS' table, which would contain the information above:

Code: [Select]


mysql> SELECT * FROM student;

+------------+------------------+
| STUDENT_CD | STUDENT_NAME     |
+------------+------------------+
| A          | ABA JONES        |
| B          | BOB THE BUILDER  |
| C          | CHARLIE BROWN    |
+------------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM class;

+--------------+----------------------+
| CLASS_CD     | CLASS_NAME           |
+--------------+----------------------+
| ENG          | ENGLISH              |
| METHODS      | MATHEMATICAL METHODS |
+--------------+----------------------+
2 rows in set (0.00 sec)

mysql>

Now, consider how you would implement the fact that a) a student can have many classes and b) a class can have many students. Note that we do not know *exactly* how many people a class will have with certainty, so that rules out adding extra fields (studentA, studentB ...studentn) and making it a foreign key. The same is true for the reverse.

This is also bad normalisation (well-forming a database) practice.

Nor can we have a class foreign key in the Student table and have multiple Student records the more classes they are in as this would violate the primary key's uniqueness.

If we set both the Class foreign key in the Student table AND the Student's ID as a composite primary key, this will work (and vice versa). However we will run the risk of what are known as data redundancy errors. Take this for example:

Suppose student A were enrolled in both ENG and METHODS. We have added a composite primary key field to the Student table 'Class_cd' which is also a foreign key to the Class table. The table should now look like this:

Code: [Select]

mysql> SELECT * FROM student WHERE student_cd = 'A';

+------------+------------------+--------------+
| STUDENT_CD | STUDENT_NAME     | CLASS_CD     |
+------------+------------------+--------------+
| A          | ABA JONES        | ENG          |
| A          | ABA JONES        | METHODS      |
+------------+------------------+--------------+
2 rows in set (0.00 sec)

mysql>

I now want to change student A's name as they've become married. While doing a blanket 'change name to 'ABA RODGERS' against all student As, we run the risk of a program or database user inadvertently changing just the one. Now we have inconsistent data.

The 'best practice' solution is similar to the above, but to create a NEW table to achieve it. This is known as the linking table. This is simply a table that has foreign keys from Class and Student, but both combine to be a composite primary key (to ensure uniqueness between each 'instance' of a Student's participation in a Class).

Going back to the tables as they were before:

Code: [Select]


mysql> SELECT * FROM student;

+------------+------------------+
| STUDENT_CD | STUDENT_NAME     |
+------------+------------------+
| A          | ABA JONES        |
| B          | BOB THE BUILDER  |
| C          | CHARLIE BROWN    |
+------------+------------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM class;

+--------------+----------------------+
| CLASS_CD     | CLASS_NAME           |
+--------------+----------------------+
| ENG          | ENGLISH              |
| METHODS      | MATHEMATICAL METHODS |
+--------------+----------------------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM class_instance;

+------------+--------------+
| STUDENT_CD | CLASS_CD     |
+------------+--------------+
| A          | ENG          |
| A          | METHODS      |
+------------+--------------+


Relationship:

(Image removed from quote.)

The use of the linking table will allow the database to remain consistent whilst expressing the fact that a Student may have many classes, and a Class may have many Students. The data (as in, if you wanted to retrieve the class listing with proper student details) can be re-retrieved by using a concept known as 'joins'. The Student table can be joined onto the Class_Instance table where Class_Cd = 'ENG', for example.

You should do a Dip Ed. and become a teacher. Good IT teachers are a rarity these days.
What I'm a bit iffy on is design tools, not really sure when like an appropriate tool should be used hence I screw up in the justification of suggesting one.

[excal]

Does anyone have a solid definition for:

- lag/slack time
-task dependencies

I think for the purposes of VCE IT:A, you can call lag/slack time as one and the same. Technically, there is a slight difference.

Slack time refers to the amount of time that an activity (off the critical path) can be delayed by without delaying the entire project (this is known as positive slack).

Lag time refers to the amount of time an activity needs to wait before proceeding onto one of its successor (follow on) activities. This is generally due to the successor having constraints from other predecessor activities.

Most of the time, they will be the same.

Task dependencies, also known as predecessor activities, of a given activity are activities that must be completed before the activity can commence.

[micaa]

is it a bad idea to do the entire exam in pencil, cause it doesnt say anywhere that we can't?
or would it just be logical sense to write section B in pen?

[Athomas]

Do it in pen.

Thanks for reminding me to bring a pencil, I hate pencils, forgot one in methods today as well.

LOL.

[micaa]

yeh i think i will, thanks
im the complete opposite, i love pencil
did u do ur methods exam in pen?

[micaa]

do u mean pencil?

[Kairubin]

Unless you are a very neat writer use pen. Examiners prefer pen over pencil because generally pencil will smudge. Whether by you, manhandling by your supervisor or in transit it generally does smudge. Also it's advisable to write in pen and put a single line through it if you've made a mistake. This way if your original answer was actually correct you have a higher chance of getting marks. If you are going to write in pencil be sure to use a pacer or sorts.