1
Q
what is a database
A
- An organised collection of data (persistent organised store of related data)
2
Q
what does organising data in an electronic database allow for? (advantages)
A
- easier + quicker adding, modification, deletion, updating and searching
- easier to back up data
- can be accessed by multiple people at the same time from different locations
3
Q
what is data
A
- information stored which can to be personal in some cases
- it can be collected and analysed
4
Q
what is information
A
- facts and details about a certain thing in context.
5
Q
what is knowledge
A
- something humans obtain/acquire and remember by reading or searching up topics to broaden understanding.
6
Q
what is a relational database
A
- Where data is stored in tables grouped by entity and linked (related) together.
7
Q
what is a relationship and what is needed in both tables for it to work
A
- link between tables
- we need a common field in both tables for relationship to work
8
Q
when designing a relational database and linking tables, relationships come in what 3 forms?
A
- one-to-one
- one-to-many
- many-to-many
9
Q
what do we use to sketch the relationships between tables
A
- entity-relationship diagram (ERD)
- can also call it entity-relationship model
10
Q
what is a flat file database. what is a suitable use for this type of database (think in terms of quantity of data)
A
- A database with multiple independent tables or single table
- no links/relationships between tables
- suitable to store small amount of data e.g contact details, small product database, maintain game/music collection
11
Q
what is a flat file database normally saved as
A
- a comma-separated values file (CSV)
12
Q
what are the positives to a flat file database
A
- simple + require little expertise to maintain
- quick to set up
- all records stored in one place
13
Q
what are the downsides to a flat file database
A
- no links –> inefficient
- can become difficult to maintain, expand in future and update, less secure
- not easy to query - searching slower
- data can be easily duplicated (take up unnecessary storage space due to redundancy)
14
Q
what are the advantages of a relational database (multiple diff. tables linked together using relationships created by primary and foreign keys)
A
- Data Integrity maintains consistency, accuracy and reliability of data
- referential integrity can be enforced which improves data integrity
- Linked tables makes it easier to query, add, modify, delete, update, search and manage/maintain
- Easier to change format
- Provides security features - keeping data secure is of high importance
- Normalised to 3NF
- Ensures less data duplication therefore less redundant data reducing file size
15
Q
drawbacks of relational database
A
- more difficult to set up and need more technical expertise to do things like normalisation
- data spread out between multiple table. some tables may be link tables which only display key fields / references
- more expensive as DBMS required
16
Q
what is a primary key
A
- field in a table that is unique for every record
17
Q
what does the primary key ensure for each record
A
- primary key ensures that each record is distinct from the others.
18
Q
what is a foreign key
A
- it’s the unique primary key field of one table that is stored in another for purpose of creating a link between the tables.
(linking field in a table that is a primary key in a related table)
19
Q
fill the gaps:
- a foreign key value must have a corresponding _________ ____ value in another _____
A
- primary key
- table
20
Q
In order to combine information from two tables, there must be a what?
A
- there must be a primary/foreign key pair.
21
Q
what are composite keys are made up of.
A
- more than one attribute
22
Q
give an example of composite key used for taking one school course
A
- none of the attributes on their own (Subject and StudentID) can be guaranteed unique.
- But, a student can only enrol for a subject just once so combination of Subject and StudentId will be unique.
- Combining these two attributes will form a composite primary key. (to uniquely identify a record)
23
Q
what is a secondary key
A
- a field by which records are likely to be searched and is therefore indexed
24
Q
what is meant by “indexed”
A
- process of creating a linked list (database index) to improve speed of data retrieval operations on a dataset table at the cost of additional writes and storage space to maintain the index data structure.
25
why do we consider using secondary keys
- we may wish to search by field other than primary key
- filed being indexed takes up extra space but speeds up searching
26
what is an entity
what are the 2 types of entity existence (1st begins with p and 2nd begins with c)
- real world object that we want to store data about.
- physical existence e.g. a customer / product
- conceptual existence e.g. an order / booking
27
There is a standard notation for describing entities. what is it
- standard notation for describing entities:
EntityName (PrimaryKey, attribute1, attribute2, attribute3, ...)
28
how is each specific entity uniquely identified (use of what key and what is it)
Each specific entity is uniquely identified by a primary key.
- an attribute, or set of attributes, that will allow that entity to be identified
29
what is an attribute
- A property of an entity.
30
each attribute will have a specific what?
- data type
31
what is a record
- All fields relevant to an entity (row of table)
- stores data relevant to specific entity
- also called tuple
32
within a table, we should make sure each record is what
- uniquely identifiable
33
if each record within a table needs to be uniquely identifiable, what must there be at least one of
- one field (column) in each record (row) that is guaranteed to be unique
- this field is known as primary key
34
what is a field and what does each column represent
- column in a table
- each column represents an attribute
35
what are serial files
Serial files: I.e. bank statements (data stored in order entered, no order maintained)
36
what are sequential files
Sequential files: data stored in order of key field
37
if identification of a suitable primary key field is more difficult, what is the solution?
- solution = allocate a number as the primary key (e.g. student ID, employee ID).
38
Most database management systems will allow you to specify that a primary key field is what?
- Most DBMS's will allow you to specify that such a field is auto-incremented (for the next record).
39
It is also possible to have a primary key that is made up of more than one attribute. What is the technical name for this?
- primary key made up of more than one attribute = a composite primary key.
40
what is a set?
- collection of distinct elements / collection of records stored in a table.
41
what do databases avoid and what can they have different levels of
- databases avoid redundancy
- can also have levels of access for different users
42
what is data integrity
- refers to process of maintaining consistency, accuracy + reliability of data in a database
- is of prime importance in any computer system
43
What main technique can help ensure data integrity in a relational database.
2 extras
- referential integrity
extra: Validation and verification techniques
44
what can cause reduced data integrity
- duplicate data
- inaccurate data (information produced from systems with inaccurate data will be discredited)
45
what is Referential Integrity.
– accuracy + consistency of data within a relationship, when data is referenced.
- Ensuring that changes are consistent across a database e.g if a record is removed, all references to it are removed.
46
what does referential integrity prevent from happening
- prevents operation that could damage relationships between tables (e.g. deleting a table that is linked to another in a database)
47
What is the benefit of enforcing referential integrity on relational databases and why?
- improving data integrity with relational databases, by enforcing referential integrity.
- doesn’t cause problems between linking tables and primary keys
48
Fill the gaps: referential integrity
the underlying system will ensure that when a _______ is added to a table and a value is entered into a _______ key field, the value exists in the ________ key field of the related table.
- record
- foreign
- primary
49
what is a database management system (DBMS)?
And what does it ensure?
- a software package that allows a database administrator to maintain one or more relational databases.
- ensures data stored in database remains consistent
50
describe some features of a Database Management System
- allows different apps to access data at same time
- provide backups +ability to restore backup
- controls access to data (security features provided to limit who can do what)
- supports a query language used to extract, add + amend data and alter database structure
- can enforce referential integrity and controls concurrency (can lock data while someone working on it so data isn't amended at same time)
- hides complexity of physical implementation (allows the administrator to define the database structures at a conceptual or logical level)
51
why is there a need to separate the database from the program
(hint: explain why DBMS is regarded as a guardian of the data and what this means apps can't do + the implication of it if that scenario did happen)
- DBMS acts as guardian of the data and any app needing to access data has to do so via guardian. This prevents apps from handling data wrongly which could compromise integrity of database
- if code of programs are edited, programmers don't need to worry about compromising data (it's stored elsewhere)
52
what is a query language and give example
- commands an app will use to reference database and extract, update, delete or add data
- SQL
53
when it comes to retrieving data, an app is querying the database.
What does this mean
- querying the database means asking it questions to find required data
54
what is a dependency
- every other field depends on primary key
55
what is a partial dependency
- one or more of fields depend on part of primary key
- arises when a table has a composite key
56
different database queries happening often results in multiple what?
- multiple transactions taking place
57
what should the transaction process never cause and why
- a database to become inconsistent or corrupt
- if database becomes inconsistent, we can no longer guarantee accuracy
58
what does it mean if a cascade delete restrain is enforced on the primary key relationship between tables
- means referential integrity is maintained
- if a record is deleted from one table, any associated rows from another table are also deleted
59
what is a Transaction
Sequence of database operations treated as a single, logical unit of work.
A transaction can be single operation but most = multiple steps.
60
What 5 problems can arise from transaction processing? (CIDDD)
SEE NOTES FOR DEFINITIONS OF THESE
Concurrency
Isolation
Deadlock
Data Integrity
Durability
61
Solutions to overcome problems that arise in transaction processing
SEE NOTES FOR DEFINITIONS OF THESE
Locking
Deadlock Prevention or Deadlock Detection
Logging and Recovery
Commit and Rollback
Two-Phase Commit Protocol
Concurrency control (Techniques are Locking and Timestamping)
Transaction management
62
what is Concurrent Processing
A concurrent request is one that is made at the same time as another.
63
how is concurrent processing managed
managed by use of serialisation, record locks, commitment ordering and timestamp ordering.
64
what is Serialisation
concept that, when two or more transactions are executed concurrently, the effect should be the same as if they had been executed serially.
65
what is Record locking
common method to allow concurrent transactions by locking records.
66
what does ACID stand for?
Atomicity, Consistency, Isolation and Durability
67
1NF
1 value per cell (values in fields should be atomic)
No 2 records identical
Field names unique (all)
Each table - primary key
Values in fields from same domain (unable to be further broken down)
(1NF EV)
68
2NF
All partial dependencies should be removed
A partial dependency is one on part of a composite key.
69
3NF
All transitive dependencies should be removed
A transitive dependency is one on a field that is not the primary key.
computer science ocr a level
flashcards
Decks in class (17)
# Cards
-
1.1.1 structure and function of processor120
-
1.1.2 types of processor43
-
1.1.3 lesson 1 input, output and storage devices76
-
rest of 1.1.3124
-
1.2.1 systems software102
-
1.2.1 systems software (virtual machine exam q's)7
-
1.2.2 applications generation101
-
1.2.3 software development70
-
1.2.4 types of programming language34
-
1.3.1 exams q's: compression, encryption and hashing11
-
1.3.2 databases69
-
1.3.3a and 1.3.3b networks52
-
1.3.3c, 1.3.3d and 1.3.3e networks83
-
1.3.4 web technologies8
-
parallel and concurrent processing (the difference)2
-
1.5.1 computing related legislation UNFINISHED16
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Year 13 mock22
