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Keys
Primary Key: a field in a table that uniquely identifies each record in the table.
Super Keys: combination of fields in a table which uniquely identify each row
Candidate Keys: Minimal Super key, all possible options for the primary key
Primary Keys: Minimal candidate key that uniquely identifies a record. A candidate key chosen for its
simplicity.
Composite/compound/concatenated Keys: The combination of two or more fields to form a primary
key.
Normalization avoids:
1. Repeating groups- produce invalid tables because of infringements on primary key
• type 1: occurs when a field contains more than one value
• type 2: multiple fields storing the same value
2. Data Redundancy-Where the same piece of data is stored in multiple cells. Occurs when
repeating groups are removed.
3. Anomalies-
• Update: Occurs when the same data needs to be updated in more than one place.
• Deletion: Occurs when a deletion causes unnecessary loss of data.
• Insertion: Occurs when records are added that do not satisfy the primary key.
4. Complex Queries
Process of Normalization
Definition: Normalization is the process of dividing a set of data into smaller tables using a defined
set of rules.
3 Forms studied:
• 1NF (normalization form)
➢ No repeating groups
➢ Choose a primary key
• 2NF
➢ Relation is in 1NF
➢ No partial dependencies
• 3NF
➢ Relation is in 2NF
➢ No transitive dependencies
,Dependencies:
Dependency: Where one field is related to the other
Partial dependency: When a fields value is dependent on only part of a composite key.
Transitive dependency: When a fields value is dependent on a non-key field.
Data:
Derived data: When you use a field to calculate another.
E.g. deriving a person’s age from their birthdate
Duplicate data: When a record has the same value for a field as another record.
E.g. two students lived in the same road or had the same surname
Atomic data: Each value of a field should store a single data item and should not be combined.
E.g. storing the person’s name and surname in the same field in non-atomic data
Referential Integrity :
The idea of not having data that refers to other data that does not exist.
Alternative method of normalization
1. One-to-one (1:1)- put both fields in the same table
2. One-to-many (1:n)- add a foreign key to the table on the many side which is the primary key
of the table on the one side
3. Many-to-many (m:n)- Creates a new link table with a combination primary key using the
primary keys of the other two tables
, IT Theory Chapter 2– Hardware and Software
Modular Design- Computers are built with these which means that they can be put together in
pieces with personalized requirements in mind. Unlike a single unit where hardware is fixed.
Advantages:
• Repairs- in a modern computer it is a simple task to remove the offending power supply and
replace it with a working unit.
• Upgrades- modular design simplifies the upgrading of the computer with better hardware.
• Flexibility- modular design allows for a variety of components to be added to the mother
board depending on the user’s needs.
Techniques for improving processor cache
Hyper threading Allows the next instruction to be preloaded into a second set of
registers while the first set of registers is being processed reducing
the time it took to switch between instructions.
Multiprocessing Having multiple CPU’S called cores on a single CPU chip. The entire
core is duplicate don the CPU chip instead of only duplicating the
registers.
Processor Cache Small but extremely fast memory storage that is integrated directly
into the CPU. It helps reduce the time it takes for the processor to
access frequently used data, improving overall system performance.
Register Size Indicates how much information the processor can operate on at
one time and how it moves data around internally within the chip.
Bus Size The more signals sent simultaneously along the data bus, the more
data is transmitted therefore wider address busses allow for more
memory addresses to be addressed.
Overclocking/ Clock The practice of making computer components run at speeds faster
Multiplication than designed by manipulating frequencies.
• Per component – CPU operates faster than system clock
• Whole system – System clock is increased affecting
components
Dangers:
• Components running at speeds faster than which they were
designed for may cause failures
• Increases power consumption which increases heat and
adequate cooling methods should be compensated for
Multithreading - The ability of a single process to execute multiple threads concurrently, allowing
for improved utilization of CPU resources and efficient handling of multiple tasks within a program.
Hyperthreading - Enables a single physical processor core to appear as two logical processors,
allowing for improved instruction-level parallelism and increased overall system performance.
Multiprocessing - The use of multiple physical processors or cores to execute multiple tasks or
processes concurrently, thereby enhancing the system's processing capacity and performance.
Multitasking - The capability of an operating system to run multiple applications or processes
simultaneously, dividing CPU time among them and providing the illusion of concurrent execution
for efficient user interaction.
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