class revision Flashcards
difference between redundant data and data redundancy
- redundant data is BAD(repeated data in the database)
- data redundancy is when copies of the database are made so they can be used in case something happens
when does a datanase have RI (2)
- relationships are consistent
- each foreign key links to an existing primary key
what is a foreign key
a key in another table which references the primary key
what is a constraint in a database
a set of ules set by the programmer such as defining the primary key and the foreign key.
what enforces data integrity
ACID
what happens when data moves down layers
it is further encapsulated (headers and addresses are added)
what performance modelling
when simulations are produced to model situations before implementing these into the real world
what are the advantages to caching(2)
- faster response times as data doesn’t need to be read from disk
- reduces the load on a system(fewer data access movements)
what are the disadvantages to caching(2)
- very hard to program and apply successfully
- if the wrong data is cached the program could end up running slower
what are the 4 chategories of development methodologies
- linear
- ## iterative
- predictive(documebt focused)
- adaptive(code focused)
what is a global variable
a variable which is defined in the main program
what is a local variable
a variable which is defined in a procedure/function
how does ByValue work
a copy of the variable’s data is passed into the subroutine
how does ByReference work
a pointer to the variable’s
memory location is passed
what is the purpose of the address bus
to transmit the address of data to be read from or written to RAM
where is the data stored when the address bus reads from it
in the MAR
what is the purpose of the data bus
to transmit data between CPU and RAM
what are the protocols involved in the application layer
HTTP and DNS
what is the role of the HTTP
sends requests to webpages
what is the protocol involved in the transport layer and what does it do
TCP, creates a reliable connection between the nodes and the server
what happens in the transport layer
- headers and port numbers are added to data packets
- packets are reordered as they arrive at the destination
what protocol is involved in the internet layer
IP
what happens in the internet layer
- routers use IP addresses to direct data packets across networks
- headers are added to packets
what is the protocol involved in the link layer
ETHERNET
