0.3-0.7

When data is transmitted, regardless over a network or not, it is sent in the form of a packet; a data packet is split into 3 main parts: the message, header and footer.

• a packet has a max amount of data that it can transmit, defined bytheprotocolcurrentlyinuse
• Enforce andprovideservicestoenabledatatransmission and govern the rules that apply.
• A packet can be thought of as being like an envelope, with criticalinformationaboutthedestination and sender written on the outside of it. 

Serial: connections always send one bit then another in order

Parallel: can send more than one bit at the same time.

Simplex: data can travel in only one direction

Half duplex: data can travel in both directions but only one at the time

Full duplex: data can travel in both directions at the same time.

Data transmission speeds can be increased using multiplexing; a methods where several independent data sources are combined and sent along a single route to a single destination.

• Packet and circuit switching – method of breaking data files into small packets in order to send them across the network.

Typical contents of packets: two different types of data are contained within a packet, namely the control information and actual data. The control information provides the data needed for the network for deliver the actual data.

Typically, control information is found in a packet’s header and trailer, with the actual data in between.

Network collisions – a data collision is natural occurrence on a network where two sets of data are detected simultaneously. Two transmitted packets are discarded when a collision is detected.

Datatransferrates:

Theinternetisaworldwidecommunicationsinfrastructure of interconnected packet-switched networks; these networks use the standard internet protocol.

A single bit is represented as either 1 or 0.

These bits are grouped together to represent information that is more meaningful, from small integers to complex graphics and programs.

A word is a group bits that can be manipulated as a single unit by the CPU. The size of a word usually consists of 16,32,64 or 128 bits.

Data Types:

Way of representing binary numbers as it allows you to use negative numbers without reducing the range of numbers.

The precision of floating point binary depends on the number of bits used to represent the mantissa.

Advantages and disadvantages of floating point:

Methods for dealing with a situation where there are not enough bits to represent all of the numbers to be stored.

•Fixed length record – made up of a number of field, each one having a specific data type and size •Common datatypesincludeinteger, string, date and Boolean. •Estimatingfilesizerequiresthesizeofsinglerecordsto be calculated, multiplied by the number of records and 10% added on for metadata.

Files are opened in one of three modes: append, read and write. Files are read by iterating over records using end of file to end the loop

Serialfiles– new records are appended to the back of a file. All files are stored in chronological order.

Sequential and indexed sequential files – order records based on a primary key field.

Random Files Random access involves jumping to a record directly without the need to search numerous records or use an index Hashingalgorithm will produce a position in a file; it must produce the same key every time and mustdoitregardless of what is already in the file. Direct accessfiles are split into blocks where each block contains a fixed number of records; hashing algorithm will produce a start position of the block and then a serial search can occur on the block to find the file.

Transaction files will store data collected over a short amount of time.

Master filesstoreallthedatarequiredtoperfrombatchprocessingoperations.

Process of copying files from the main area to a separate area.

Archiving is the process of moving old files to  separate system location in order to speed up the main system

The ability to holdvast amounts of information.

Flat file – data is help within a single table; each column is an attribute and each row is a record.

Relational– manysmallertables linked together

Primary key is a piece of information in each record that is unique to that record; often called a ‘uniqueidentifier’

Foreign key is any field in a table which is the primary key for another table.

• Entity integrity – every table must have a primary key which is unique and not empty
• Referentialintegrity – foreignkeysmustpointto the primary key of another table but can be empty (meaning there is no relationship)
• Domain integrity – all attributes in the database are related to the overall domain that the database is working on.
• Normalisation is the process of converting a flat file into a relational database.
  • Different stagesofnormalisation: the most common is 3NF which contains no transitive dependencies
• Indexing is a data structure used to shorten the length of time it takes to search a database
  • For exampletheindexmightcontain aspecific column

Database views allow a restricted view of the entire database for performance and security reasons DMS allow users and databases to be managed

• Databases are servers that run in the background and have no user interface

Contains thenetworkaddressoftheserver,username, password, schema name

Distributeddatabasessplitanorganisation’sdata need between multiple servers.

Data warehousing(datamining) – allows analysis of big data to uncover patterns and predict future outcomes. –Fraud detection: data mining has enabled company to spot suspicious transactions –Requires fairly advantaged technology  and a large amount of data to be accurate