Exchanging Data Flashcards
Lossy
Unnecessary info removed
Reduce in quality
JPG, MP3
Lossless
Recording patterns in data rather than actual data
PNG, Zip
Run length encoding, dictionary based compression
Symmetric Encryption
Private key
Same key to decrypt and encrypt
Diffie Hellman key exchange
Can be intercepted
Asymmetric Encryption
Public key 2 keys (public: decrypt, private: encrypt)
Digital Signatures
Verify trustworthiness I’d message
Hash value = Private key encrypts hash total
Decrypted with public key and if matches calculated hash total from sent message, genuine
Digital Certificate
Verify trustworthiness of message sender
Issued by Certificate Authorities
Primary key
Uniquely identifies entity
Foreign key
Creates relation between 2 tables
DBMS
Database management system
Software to define, manage, manipulate and retrieve data
Make forms, reports, queries
CRUD- create, read, update, delete
Normalisation
1NF- no repeating attributes
2NF- no partial dependencies
3NF- all attributes on whole key and nothing but key
Reasons for normalisation
No data redundancy Easy to modify and maintain Data integrity maintained Faster searching and sorting Records on 1 side of 1 to many cannot be deleted
SQL
Structured query language SELECT FROM WHERE ORDER BY;
WHERE … LIKE ‘a%’ or ‘_a%’;
SELECT column/s
FROM table1
JOIN table2 ON table1.column = table2.column;
INSERT INTO
VALUES;
ACID
Atomicity- transaction processed entirely or not at all
Consistency- referential integrity
Isolation- concurrent execution of transactions lead to same results if processed 1 after another
Durability- once a transaction committed, remains so
Record locks
Prevent simultaneous access to objects
Deadlock is if 2 access same record at same time
Serialisation
Transactions do not overlap in time
Time stamp ordering
Commitment ordering
