DFD

Schema

Database schemas or schematic diagrams are a technique for modelling the

relationships within a relational database. Schemas include each entity (table)

together with its attributes (field names). The primary key field (or fields) is

underlined. Lines between attributes represent the relationships or joins

between tables. Each relationship line is labelled to indicate the nature of the

join. Reducing data redundancy (wastes storage space and increases

maintenance problems). It involves designing an efficient schema and by

splitting data into tables, linked by relationships, and splitting fields into

smaller fields. Data is reorganised and repeated fields are removed.

Communication systems:

In SQL (Structured Query Language)

searching and sorting is performed

using the SELECT statement. The

general syntax of the SELECT

statement is described in Fig 2.63.

This is by no means a thorough

definition of the SELECT statement,

however it is sufficient for our

current purpose. Following the

SELECT keyword is the list of

attributes or fields that will be

retrieved – replacing this list with an

asterisk “*” causes all attributes to

be retrieved.

Transmission Level Protocol:

The Ethernet Transmission Level protocol uses an 8 bytes (64 bits) long preamble, which is simply a sequence of

alternating 1s and 0s that end with a terminating pattern (commonly 1 1) called a frame delimiter. The receiver

uses the preamble to adjust its clock to the correct phase as the transmitting clock. A frame delimiter is needed at

the end of the preamble because the receiver may lose some bits during clock adjustment, so these delimiting bits

act as a flag indicating the start of the actual data. CRC – For error checking. The sender calculates the CRC based on

the contents of the frame. If the recalculated CRC matches, the frame is accepted, or the data is resent.

Twisted pair cable, as the name suggests, is composed of pairs of copper wire twisted together. Each copper wire is

contained within plastic insulation and then the twisted pairs of wire are enclosed within an outer sheath. The

regular twists in each pair are specifically designed to limit the electromagnetic interference between pairs and also to

a lesser extent from outside sources.

Unshielded Twisted Pair (UTP) is the most common and economical form of copper cable for both LAN and telephone

connections. UTP cable does not include any physical shield against outside electromagnetic interference (apart from

somewhat limited shielding provided by the twists in each pair). Most UTP cables contain four pairs.

Shielded Twisted Pair (STP) and Screened Twisted Pair (ScTP) includes a metal shield or screen and a drain wire. STP

and ScTP cable is significantly more expensive therefore its use is limited to applications where a high level of

electromagnetic interference is present – primarily industrial applications.

Advantages – Inexpensive; readily available

Disadvantages – Susceptible to EMI; lower bandwidth; bad over long distances (100m)

Token Ring - It is used to send/receive data in a physical ring. As the token circulates, nodes attach packets to the

token and the token continues passing until the recipient receives the message. A confirmation is then attached t

the token ring and sent back.

• Coaxial Cable

Coaxial cable was originally designed to transmit analog broadcast TV from antennas to television sets. As analog T

transmit on frequencies ranging from 30MHz to 3GHz (VHF and UHF bands) the cable also needed to support these

frequencies. Furthermore, coaxial cable is relatively immune to outside electromagnetic interference compared to t

- Advantages – Less susceptible to EMI, more durable and faster data rates than TP, available

- Disadvantages – More expensive, bulkier, and less flexible than UTP; slower data rates.

• Optic Fibre Cable

Optic fibre cable is able to support far higher data transfer rates over much greater distances than either twisted p

cable.

Advantages – Higher data rates over greater distances; immune to EMI; lightweight; secure

Disadvantages – Expensive in cost & service; specialised installation

LAN apps – Each optical fibre is held in protective plastic coating like coaxial cables. The final cable is then enclosed

sheath.

- E.g. When transferring a webpage, HTTP, TCP, IP and Ethernet are involved.

Interactive media are means of communication in which

the output values depend on inputs. This means that the

user is actively involved in the communication. ... One of

the most important characteristics of interactivity is the

interaction between user and machine, where each of

them has an active role.

Content Providers

Content providers, as the name suggests, provide ready to use content. There are organisations that specialise in the

provision of stock photographs, animations, video and also text articles. These content providers act on behalf of the

copyright holders and negotiate fees so that the content can be legally used. The content provider retains a portion

of the fee and the remainder is forwarded to the copyright owner.

Storage and retrieval

Augmented reality

Augmented reality is an

interactive experience

of a real-world

environment where the

objects that reside in

the real world are

enhanced by computer-

generated perceptual

information, sometimes

across multiple sensory

modalities, including

visual, auditory, haptic,

somatosensory and

olfactory.

Virtual reality in

multimedia

VR social media is allowing multimedia

communications to reach people in exciting ways. ... The use of augmented reality and virtual reality is changingthe way that people experience various typesof media. These types oftechnology are allowing people to interact with video games, ads, films, and other multimedia forms