Day: March 25, 2010

FIT9018: Week 4

This weeks lecture was a continuation of ‘Operating System II: File Management”. Most of the concepts covered in this weeks lecture I had looked at in last weeks review.

Some of the new points introduced were:

When a file is accessed it has four id’s (I assume an example is real and sudo):
- a real user id
- an effective user id
- a real group id
- an effective group id
Standard Input, Output, Error – Every time a shell is started. 3 files are opened automatically:
- stdin, (keyboard), 0
- stdout, (screen), 1
- sterr, (screen), 2
Example of how inode numbers and logical directory structures work.
How rwx Permissions work with directories: (Pearl of the Week)
- Read- Processes can list names and subdirectories within directory
- Write- Processes can alter the directory (create and remove files). To modify files write permission must be applied to the file.
- Excecute- Allows the user to cd into the directory. To open a file or excerpter a program a user must have execute permission on all directories leading to the files absolute path name.
Hard and Soft(Symbolic) Links
Locks (not covered in detail yet)

Pearl of the week: vi/vim text editor

$ vi myfile
$ vim myfile

In the tut we worked with vi/vim text editor which is a tool I had struggled with before and had never bothered to read the tutorials on.

It turns out that it is a damn good editor as it is very very quick and easy once one becomes even moderately sufficient (2-3 hr tutorial). One of the primary advantages is that it runs within a command prompt environment so can be used via SSH with ease.

Some of the handy commands learnt in the tutorial are:

i -> insert mode
: -> comand mode
esc -> back to normal mode
CTRL + G -> End of the doc
/prase -> find phrase
n -> next phrase down
N -> next phrase up
:%s/word1/word2/gc -> replace all word1 with word2, gc adds confirmation for each occurance
u -> undo
d -> delete
put -> put was what just deleted
v -> visual select
w -> word (dw -> delete word)
$ -> end of line (d$ delete from cursor to end of line)
:set tabstop=2 -> set tab distance to 2
:set number -> show line numbers
:set nonumber -> hide line numbers
:1,4d -> delete lines 1,2,3,4

There are a great deal many useful examples of these which i shall add in as I use them.

Random

Getting iPhone working on Linux (without jailbreaking)

Post author By mark
Post date March 25, 2010
No Comments on Getting iPhone working on Linux (without jailbreaking)

Steps to Using iTunes and iPhone on Ubuntu (using windows virtual machine)

Install git, with the following command: sudo apt-get install git-core
Install iPhone connectivity the driver with the following command: git clone git://github.com/dgiagio/ipheth.git
Install VitualBox PUEL (http://www.virtualbox.org/wiki/Linux_Downloads) , ensure it is PUEL, no OSE Edition
Install Samba and share Music folder (instructions: https://help.ubuntu.com/9.04/serverguide/C/samba-fileserver.html)
Open Sun Virtual Box, create a virtual machine (ensure in vm settings USB is enabled and iPhone filter selected).
Install iTunes on the vm and access your songs through shared folder.

All up takes about 2 hrs max and is the easiest way to get your iPhone working on Ubuntu without jail breaking.

Database Technology

FIT9019: Week 4

Unfortunately I missed Manoj’s 4th lecture, the notes however are online and I will run through a summary of them.

Part 1: Normalization

Data normalization is required to ensure that a relational database will perform UPDATE, CREATE and DELETE queries without anomalies (loss of data integrity).

The process of normalization has numerous levels (1st Normal Form [1NF], 2NF, 3NF, BCNF, 4NF, 5NF) which will be shown below. Prior to running through each level, the terminology for dependencies must be clarified.

Functional Dependence: A relationship between two attributes each value of A is associated with exactly 1 value of B, ie; ID is a determinant of Name. Partial Key dependencies are determinant relationships between two or more non-primary key attributes(leading to update anomalies). Transitive Key dependencies occur when an attribute is more immediately identified be a non-Primary Key attribute/s (leading to update anomalies).

1NF: Ensuring atmoic values in the relation by removing unnecessary attributes, separating relations if repeating values occur.

CUSTOMER (cust-id, surname, initials,{order-no, order-date})
//{} signify repeating values.

Now in 1NF :

CUSTOMER(cust-id, surname, initials)

ORDER(cust_id, order-no, order-date)

2NF: Remove partial key dependencies (ensure primary key is in its minimal form and partially dependent attributes are removed to an alternate relation). Ie:

ORDER-LINE(order_number, product_no, description, number-ordered)
// As above, the description attribute is dependent only on product_no
making it a partial key dependency.

Now in 2NF:

ORDER-LINE(order_number, product_no, number-ordered)

ORDER-LINE(product_no, description)

3NF: Remove transitive keys dependencies.

ORDER(order-no, order-date, cus-id, name, street, suburb)
//name, street and suburb transitively dependent on cus-id

Now in 3NF (Transitive dependency removed by creating new relation):

ORDER(order-no, order-date, cus-id)

CUSTOMER(cus-id, name, street, suburb)
// new relation added to eliminate transitive dependency.

Boyce-Codd Normal Form [BCNF]: 3NF + only a single candidate key for each relation.

4NF: No non-trivial multi-valued dependencies. *

5NF: No join dependencies. *

* It seems we will not be covering 4NF and 5NF in this subject although other lecturers have mentioned they are the most prevalent in the business world.

That brought to a close the section on Normalization, next up was ER/EER -> Relational Model. Again as I did not attend this lecture I will just simply run through a summary of Manoj’s slides.

Inputs: ER/EER diagrams -> Outputs: relational schemas

Properties of Relations:

Each relation has a unique name..
Each tuple is unique
Attributes names are meaningful
Order of attributes is immaterial
Order of tuples is immaterial
entries are atomic (single valued)

Types of entities -> Regular(Strong), Weak, Associative(Composite).

In preparation for the transition from ER model to relation schema, the ER model must be expanded from conceptual to logical level. This involves removal of M:N relationships (Unary, Binary or Ternary) and recognition of Primary Key.

There was much more detail in this lecture but I will await the next presentation to elaborate further.