Syllabus Detail

• data anomalies, including: insert, delete and update.12 ATAR

Background

• An anomaly is something that is unusual or unexpected; an abnormality
• In technology, an anomaly can be seen as something that strays from common practice
• There are three types of data anomalies: insert, delete and update

Insert Anomaly

• An insertion anomaly occurs when data cannot be inserted into a database due to other missing data
• This is most common for fields where a foreign key must not be NULL, but lacks the appropriate data
• An example of this anomaly can be explained with a simple user database
  • A user must have a group ID as a foreign key
  • No groups have yet been created
  • Thus, a user can not be inserted in to the database as the group ID must not be NULL
• This can result in data redundancy due to the omission of data

Delete Anomaly

• A deletion anomaly occurs when data is unintentionally lost due to the deletion of other data
• For example, if a database row contained "Username" and "User Group"
  • "John" and "Fred" are in the user group "Contributors"
  • If John and Fred are removed from the database, our Contributors group will also disappear
  • This is because we haven't normalised our data, meaning the only reference to the Contributors user group lies within the same database row (or record)
  • Hence, removing the only two references of our user group results in the loss of data accuracy and integrity
• This also goes to show why it's important for us to normalise our data and how combining unlike information can be problematic

Update Anomaly

• An update anomaly occurs when data is only partially updated in a database
• A database that hasn't undergone normalisation may reference the same data element in more than one location
• As these locations haven't been consolidated and referenced, we have to make sure each location is manually updated
• This can cause problems as we then need to spend time searching for and updating each reference to the data element
• An example of this is a database containing two records; Users and Mailing List
  • John has an email address of This email address is being protected from spambots. You need JavaScript enabled to view it. in the Users record
  • John has the same email address in the Mailing List record
  • John decides to change his email preferences, which in turn updates the User record for John
  • However, the system did not automatically update the Mailing List record, leaving John with two different associated emails and thus creating inconsistencies within our database

Further Research

1. Read more about Data Anomalies from Wikia here
2. Read more about Data Anomalies from Johnstone High School here

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Syllabus Detail

• Referential, domain, and entity integrity 11 ATAR, 12 GEN, 12 ATAR

What is Data Integrity?

• Data integrity refers to the accuracy and consistency of data over its entire lifecylce
• This is a fundamental concept in Computer Science, as it can make or break an IT system
• The integrity of data is dependant on many factors, including the influence of data duplication and redundancy
• In terms of a database; referential, domain and entity integrity are assessed

Referential Integrity

• Referential integrity states that every foreign key must reference a valid existing value in another table
• This means that for every record in a normalised database, the linking element (the foreign key) must exist in another record
• Both the primary and foreign keys must be the same data type and length

Domain Integrity

• Domain integrity refers to the boundaries that shape the data entered into a database
• This can be as simple placing a limit on the length of the data item and enforcing a specific data type
• Domain integrity ensures organisation and validity in a database structure

Entity Integrity

• Entity integrity is a simple concept that ensures the validity of primary keys
• The concept states that each primary key must not be NULL (meaning it must contain a value of some sort)
• It also states that each primary key must be unique, meaning no primary key value may be the same as another primary key value in the same record

Further Research

1. Read more about Data Integrity from Microsoft here

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Syllabus Detail

• Managing data storage using files and folders. 11 GEN

Background

• The ability to manage and sort files and folders is a crucial aspect of computer systems
• Their implementation allows for organisation and ease of use
• Files and folders are essential elements to the IT world
• To read about files and file systems in more depth, check out The Computing Teacher's article on File System here

What's the difference between Files and Folders?

• A computer file is used to store data and information
  
  • All files have their own type and relative extensions
  • For example, Microsoft Office Word Documents contain the extension .doc or .docx
  • These file extensions tell the computer what program to open each file with
• A computer folder is used to store files and other folders
  • Folders are used in an organizational manner
  • They can be sorted by various attributes and are used to store larger numbers of files and other folders
  • Think of folders as filing cabinet systems of a computer, they're used to tidy up the office (or in this case, directory) by taking all papers (or files) and acting as a container for them

How can I manage my data?

• Organization is key to utilising the power of computers; make sure you stick to a naming convention and folder structure throughout your file system
• Delete any old or unnecessary files
• Sort out files and downloads as you receive them - don't wait until they're just another icon lost amidst your Downloads folder
• Create a few manageable folders (such as "Work", "Personal" and "Media")
• Always make sure to create backups of your data incase of accidental loss or corruption

Further Research

• View HowToGeek's article on file and folder organization here
• View Lifehacker's guide on data organization here

Worksheet and Practice (yet to be added)

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Syllabus Detail

• Using Chen's notation ER diagrams 11 ATAR, 12 ATAR

Step 1 - Background

• Chen's notation for entity–relationship modeling uses rectangles to represent entity sets, and diamonds to represent relationships appropriate for first-class objects: they can have attributes and relationships of their own.

  (wikipedia)

Step 2 - Vocabulary

• A disaster is 

Step 3 - Summary of Main Points

• Main point 1 is here
• Main point 2 is here

Step 4 - The Detail

 Not 

Step 5 - Further Research

1. Geek

Step 6 - Worksheet and Practice (yet to be added)

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