Lesson Notes Flashcards
CRUD instructions
Delete
Get
Post
Put
What is CRUD
an application that allows for a HTTP request to be mapped to an SQL command
REST
an architectural style
created on a web server to access a database
REST appl created and called, respond in JSON or XML
- used with javascript
- allows for a client and server to program independently
- neither know implementation details on the other side
Database Management System
Record Locks
Serialisation
Timestamp Ordering
Commument Ordering
SSD Principle of Operation
-contain millions NAND flash memory cells
(charged cell = 0, No cell = 1)
-cellls organised into pages and blocks
-data read by SSD page by page
- Updating file requires copying relevant block back to memory
(SSD become slower as they fill up as writing and updating requires copying and rewriting existing pages)
Digital Camera
Captures light through an array of photosensors
- analogue voltage represent amount of light falling on photosensor
- analogue voltage converted to digital values with an ADC
- digital value used to create pixel data for bitmap image
- each pixel colour represented using specific number of bits (determines range of bits and colour depth)
Vectors
can use a dictionary when mapping
OA = (rx,ry) R^2 (2 = dimension)
Convex Combination
W = aU + bV
where a + b = 1
example:
u = (2,2) v = (6,-2) w = (4,0)
2a + 6b = 4
2a - 2b = 0
then simultaneous equation
angle between 2 vectors
if angle > 180 then 360- angle
u.v = |u|.|v|cos(theta)
theta = inversecos(u.v/|u|.|v|)
Hash Function requirements
- generate numeric value from key
- minimise collisions (generate unique index with specific range of values)
- uniform spread of indices(no clustering of entities)
- non complex algorithm(keep execution speed low)
Mid Square Method - square item and take middle middle portion
MOD to calculate address
Folding Method
Hash Table Requirements
- number of assigned slots need to exceed num records by a third
- if hash table/file size > 70% resize it
when dealing with collisions either rehash or chain
(find next available slot(linear search) or create link list)
Digital Signatures
= hash value
FLIP-FLOP
- commonly used for data storage - store single bit of data
- used in a digital circuit for synchronisation(ensure data transfers at correct times)
- used in frequency division (clock frequency / 2)
- used in shift registers (help shift data bits in sequence)
- Input = clock/trigger/enable
Used for = update the output to the current status of the input
Full Adder
Used for arithmetic sum of 3 bits
2 significant bits and one carry over bit from prior addition
