DBMS (Data Base Management System)
Definition of DBMS:
A software system that facilitates the creation and maintenance and use of an electronic database.
DBMS overcomes a concurrent update problem by only allowing the first user to log on to update the database, any other users that log on after will only have read-only rights. This avoids the problem of 2 users trying to update the same data simultaneously. This is called RECORD LOCKING.
The database server queries from client stations and then sends back the results of the queries.
Offers DBMS facilities with object-oreintated programming.
Reasons why a software system will need updating:
- Updates in the Hardware that a systems runs on.
- To fix bugs and errors in the program code.
- Parameters change (Such as VAT rate).
- Requirements change.
DDL (Data Definition Language)
DDL Statements are used to create fully normalised tables necessary to implement a database.
When stating each entity is declared with either VARCHAR(num)
The Primary Key must have PRIMARY KEY written after it.
E.g. InventoryID VARCHAR(10) PRIMARY KEY
If the table has more than one primary key and a forgein key they must be declared at the end.
E.g. PRIMARYKEY(EquipmentID, InventoryID)
Question will ask you to make an SQL statement using commands SELECT, FROM, WHERE and ORDERBY with others.
SELECT is used at the begining of the SQL statement to declare which fields are going to be used. Each one must be written as: table.fieldname
FROM is used after SELECT to state which table the fields come from.
WHERE is used after FROM to state the conditions of the command:
e.g. table1.field1 > table2.field6.
If there is a forgein field this is also declared in the WHERE statement:
e.g. table1.fieldID = table2.fieldID.
ORDERBY is used at the end of the statement to order the results.
e.g. ORDERBY fielsID (ASC/DESC)
Fact Finding Techniques
A systems analyst can use a number of fact finding techniques:
Survey when users are interviewed to indentify what need to be achieved in the new system.
Observation of a specific area of the current system to find out how it currently work and how it ned to be improved.
Interview with key staff members to find out flaws of the current system and what the new system needs to do.
Examination of Documentation to identify how the program currently functions and what the new system needs to achieve.
Different Handheld Input Systems:
- Barcode Reader
- Smart Card Reader
- Thermal Printer (Burns on printing, like a receipt)
- RFID (Radi Frequency Identification)
- Optical Character Reader/Recognition (Scan which recognieses individual letters.)
<Head> text </Head> shows the "text" in heading bar of webpage.
<BODY> is the opening tag of the main body of the page.
<H1 ALIGN = "CENTRE"> Text </H1> This centre the words Text, </H1> ends the line.
<BR> is out at the beginning of each line of text.
</HR> draws a line across the page.
<B>text</B> makes "text" bold.
</Body> closes the body of the text.
LANs and WANs
LAN - Local Area Network - A network over a small geographical area.
WAN - Wide Area Network - A network based over a large geographical area.
Node - Device connected to the network.
Segment - A run of Ethernet cable to which are attached a number of devices.
Frame - Ethernet term for a packet.
A MAC address is a hardware address that uniquely identifies each node of a network.
Ethernet - Hubs and Switches
An ethernet can use both HUBS and SWITCHES.
HUB: A collision domain involves all computers connected to hub.
SWITCHES: Collision domain limited to 2 computers.
A HUB sends broadcasts packet (or frame) to all computers, a SWITCH sends packet (or frame) to the reciever. A SWITCH is faster than a HUB because the collisions are reduced.
Why are firewalls needed if a comany want to connect to the Internet:
- to prevent unauthorised access to a private network.
- to block internal access to specific external sites. (i.e. Facebook on school networks)
- to prevent unwanted intrusion from outside the network.