11)Define Lossy compression
2)Define Lossless compression
3)Define compression
1)where unnecessary information is removed from the original file.
2) retains all information required to replicate the original file exactly.
3)used to reduce the size of one or more files.
21)Cons of Lossy compression
2)Cons of Lossless
3)Pros of Lossless
1)compressed comes at the cost of quality-normally won't realise
2) is normally bigger file than lossy but still smaller
3)No data is lost
31) Define Run Length Encoding
2)Effect?
3)Dictionary-based compression techniques
1)it records its value and the number of times it repeats.
2)would reduce the data necessary to store
3)The compression algorithm searches through the text to find suitable entries in its own dictionary (or it may use a known dictionary) and translates the message accordingly.
41)Define Encryption
2)Define plain text
3)Define cipher
1)transformation of data from one form to another to prevent an
unauthorised third party from being able to understand it. -known as ciphertext.
2)original data or message
3)encryption method or algorithm
51)Define Key
2)Define Caesar cipher
3)Con of Caesar cipher
4)is the vernam cipher breakable?
1)secret information to lock or unlock the message
2)type of substitution cipher and works by shifting the letters of the alphabet along by a given number of characters
3)only 26 different possibilities.
4)only cipher still proven to be unbreakable.
61) Define One time pad
2)How does recipient get key
1) randomly generated private key is used only once to encrypt a message that is
then decrypted by the receiver using a matching one-time pad and key.
2)meet in person to securely share the key and destroy it after encryption or decryption
71)Define cryptoanalytic attack
2)Define Symmetric encrytion(private key)
3)Con of Symmetric encrytion
1)Type of known plaintext attack that uses a linear approximation to describe how a block cipher works
2)Uses thesame key to encrypt and decrypt data.
3)Key must be transfered to same destination as cipher text -intercepted easily
81)How does Asymmetric (public key) encryption works?
1)• One key, known as the public key, is made public so that others wishing to send you data can use this to encrypt the data
• This public key cannot decrypt data.
• Another private key is known only by you and only this can be used to decrypt the data.
91) Define Hashing function
2)how work
3)Use?
1)function provides a mapping between an arbitrary length input and a usually fixed length or smaller output.
2) one-way; you cannot get back to the original.
3)storing encrypted PINs and passwords so that they cannot be read by a hacker.
101)What is digital signature/hash value
2)How works
1) the equivalent of a handwritten signature or security stamp, but offers even greater security.
2)signature attached to the message to be sent and whole message , digital signature also ,encrypted using recipient's public key before sent.
The recipient decrypts message using their private key, and decrypts digital signature using sender's public key.
The hash total is then reproduced based on the message data and if this matches the total in the digital signature,
111)Use of digital certificates
2)What do digital certificates include
1)the trustworthiness of message content /message sender/website.
2)certificate's serial number, expiry date, name of the holder, copy of their public key,
digital signature of the CA so that the recipient can authenticate the certificate as real.
121) Define Entity
category of object, person, event or thing of interest to an organisation about which data is to be recorded.
E.g.Employee, Film, Actor, Product, Recipe, Ingredient.
Each entity in a database system has attributes.
131)Define Flat file database
2)Example of use
1)Consists of a single file.
2)Hold the names and addresses of all members of a sports club, or information about all the DVDs in your personal collection.
3)Can not have more than one entity, and relationships between the entities
141)Define Primary key
2)Define Secondary key
1)identifier which uniquely identifies the entity(s)
2)key that holds the physical location of a record or a portion of a record in a file or database, and
provides an alternative means of accessing data. Also known as alternate key. such as by using someones surname
151)Define index
1) common method for keeping track of data so that it can be accessed quickly.
Like an index in a book, it is a list in which each entry contains the name of the item and its location
161)Define one to one relationship
1) Define One to many relationship
3)Define Many to Many Relationship
1)one parent record or field has either zero or one child record only.E.g.Country and Prime Minister.
2)one entity can be present in many different instances of another entity.E.g., Borrower and Library Book
3)multiple records in a table are associated with multiple records in another table.E.g. Film and Actor.
171)Define entity relationship diagram
2)Define relationship database
1)diagrammatic way of representing the
relationships between the entities in a database.
2)collection of tables in which relationships are modelled by shared attributes
181)Define Foreign Key
2)How link many to many tables
1) attribute that creates a join between two tables. It is the attribute that is common to
both tables
2)Extra table is added into the middle to to link them e.g student to enrolment to course
- attribute of a primary key of one of the tables, known as foreign key in the second table.-common attribute
191)Define Composite key
1)A primary key which consists of more than one attribute
201)Why use entity relationship diagram
2)Example?
1)frequently involve many different entities linked to each other,
and an entity relationship diagram can be drawn to show all the relationships.
Ward, Nurse, Patient and Consultant. ward is staffed by many nurses, but nurses works on only one ward.
211)Define referential integrity
particular component is not deleted if it is used in a product in the Product table.
221)key to understand to read or write relational databases
1)Entity name is shown outside the brackets
The attributes are listed inside the brackets
The primary key is underlined
231)Define index
1)when the database is created, for any attribute that is often used as a search criterion.
241)Define normalisation in relational databases
1)process used to come up with the best possible design for a relational database
251)How should a relational database be organised?
1)no data is unnecessarily duplicated (same data item held in more than one table)
data is consistent throughout the database (e.g. a customer is not dif info in dif table
table is flexible enough to allow you to enter as many or as few items
make all kinds of complex queries relating data from different tables)
261)What is 1st normal form in relational databases
2)What is 2nd normal form
1) it contains no repeating attribute or groups of attributes
2)it is in first normal form and contains no partial dependencies.
271)Define partial dependences
1)one or more of the attributes depends on only part of the primary key,
which can only occur if the primary key is a composite key.
281)Define 3rd normal form?
2)Define non key dependencies
1)if it is in second normal form and contains no 'non-key dependencies
2)one where the value of an attribute is determined by the value
of another attribute which is not part of the key.
-All attributes are dependent on the key, the whole key, and nothing but the key.
29importance of normalisation
remove the possibility of redundant data from any of the tables-saves space
maintain and change ,Data integrity is maintained since no unnecessary duplication of data.
produce smaller tables with fewer fields=faster searching
not allow records table on 'one' side of a one-to-many relationship be deleted accidentally. -if have unresolved file
301)Define redundant data
1)Redundant data is data that appears in more than one database table,
which can cause inefficiencies and inconsistencies in the data
311)Define SQL
1)Structured Query Language is declarative language used
for querying and updating tables in a relational database.
It can also be used to create tables.
321)Define SELECT
2)Define FROM
3)Define WHERE
1) list the fields to be displayed
2)list the table or tables the data will come from
3)list the search criteria
331)Define ORDER BY
1) list the fields that the results are to be sorted on
(default is Ascending order)
351)what does * mean in SQL ?
2)SQL statements are written what format?
1) Display all fields in the record
2)SELECT *
FROM table
WHERE condition
361)how write SQL if more than one table is involved?
2)Example
1) SQL uses the syntax tablename . Fieldname
Song.ArtistID = Artist.Artist ID provides link between t Song and Artist tables so that the
artist's name corresponding to the ArtistlD in the Song table can be found in the Artist table
371)What does JOIN do in in SQL
1)provides an alternative method of combining rows from two or more tables
based on a common field between them
381)Does it matter if in SELECT statement if already connected?
1)No
391)Define CHAR(N)
2)Define VARCHAR(n)
1)Character string of fixed length n
2)Character string variable length,max,n
401)How add coloum to table
2)How delete coloum to table in SQL
1)ALTER TABLE Employee
ADD Department VARCHAR(10)
2)ALTER TABLE Employee
DROP COLUMN HireDate
411)How to change datatype in table on SQL
ALTER TABLE Employee
MODIFY COLUMN EmpName VARCHAR (30) NOT NULL
421)What does INSERT INTO mean?
1)used to insert a new record in a database table. The syntax is.
INSERT INTO tableName (columnl, column2, …)
VALUES (value1, value2, …)
431)What does UPDATE mean in SQL
1)used to update a record in a database table. The syntax is:
UPDATE tableName
SET column1 = value1, column2 = value2, …
WHERE coIumnX = value
441) what does DELETE mean in SQL?
used to delete a record from a database table. The syntax is:
DELETE FROM tableName
WHERE column = value
451)is data gathered deepnding on criteria
1)Yes, may be selected before it is even added to a database, whether or not it matches specified criteria.
E.g. speed camera may automatically photograph only those vehicles which are exceeding the speed limit
461)Define EDI
1)Electronic data interchange (EDI) the electronic transmission of by agreed message standards
from one computer system to another without human intervention.
a system for exchanging business documents with external entities.
471)Define ACID
1)ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that
guarantees that transactions are processed reliably.
Atomicity- requires that a transaction must be processed in its entirety or not at all
481)Problems of multi user database?
1)data can be lost ,lose updates
491)Define Record locks?
2)Cons
1)preventing simultaneous access to objects in a database in
order to prevent updates being lost or inconsistencies in the data arising
-if anyone attemps to access same time is denined
2) two users attempt to update two records, situation can arise which neither proceed- deadlock.
501)Define Serialisation
2)Why does timestamp ordering occur?
1)ensures transactions do not overlap in time and therefore cannot
interfere with each other or lead to updates being lost
2)so that if two transactions affect the same object (for example record )
transaction with the earlier timestamp should be applied first.
511)Define commitment ordering?
1)ensure that transactions are not lost when two or more users are simultaneously trying to access the same database object.
Transactions are ordered in terms of their dependencies on each other as well as the time they were initiated.
521)Define Redundancy
1) to prevent or recover from the failure of a specific component or system-by having mulitple servers