Key term
WJEC A-Level Computer Science 601-5345-3
Hardware: Architecture, Memory and Storage
Networks and Data Transmission
Logic Gates and Boolean Algebra
Data Representation and Data Types
Data Structures
Organisation of Data: Files and Records
Database Systems
The Operating System
Algorithms and Programs
Principles of Programming
Systems Analysis
Software Engineering and Program Construction
Topic overviewIntegrated development environments and their purposeEditors, syntax highlighting and code entry toolsDebugging tools: breakpoints, stepping and watchesTranslation, source code and object codeLexical analysis and the symbol tableSyntax and semantic analysisCode generation and optimisation
Types of Software System
Practical Programming
Data Security and Integrity
Computing, Society and the Law
Topic overviewSocial and economic change from computingComputers and the nature of employmentThe digital divide and cultural changeEnvironmental cost of computingData protection and freedom of information lawThe Computer Misuse Act 1990 and computer crimeCopyright, surveillance and professional codes
Advanced Data Structures and Logic
Recursion, Sorting and Searching
Programming Paradigms and Translators
Topic overviewFunctional, declarative and imperative paradigmsClasses, methods and object-oriented designStandardisation of computer languagesAmbiguity in natural language and unambiguous notationBackus-Naur form and syntax diagramsCompilers, interpreters and assemblersTranslation and execution errors
System Design and Human-Computer Interaction
Software Engineering Tools and Professional Practice
Topic overviewSoftware tools for the software engineering processSoftware packages in systems analysis and specificationSoftware packages in systems designTesting tools and testing strategiesProgram version managementProgram libraries and project management toolsCodes of conduct and professional behaviour
Advanced Architecture and Assembly Language
Communication Networks and File Organisation
Number Representation and Floating Point
Databases and Distributed Systems
Topic overviewConsistency, redundancy and data independenceRelational organisation and normalisationRestructuring data into third normal formEntity relationship modellingQuery languages and SQLValidation, verification and the DBMSBig Data, data warehousing and miningDistributed systems and distributed databases
Operating System Management
Software Systems and Applications
Data Security, Cryptography and Attack
Databases and Distributed Systems
- 8 subtopics
- 24 things to know
- A2 Unit 4
What Databases and Distributed Systems covers
Databases and Distributed Systems is examined in A2 Unit 4, Computer Architecture, Data, Communication and Applications. It covers consistency, redundancy and data independence, relational organisation and normalisation, restructuring data into third normal form, entity relationship modelling, query languages and SQL, validation, verification and the DBMS, big Data, data warehousing and mining and distributed systems and distributed databases.
Where it is assessed
A2 Unit 4
Computer Architecture, Data, Communication and Applications.
Check the WJEC specification ↗The 8 subtopics
Each one has its own page.
- Consistency, redundancy and data independenceData consistency, data redundancy and update anomaly.Open →
- Relational organisation and normalisationRelational database, primary key and foreign key.Open →
- Restructuring data into third normal formRecall questions on the key, the whole key and nothing but the key, worked repairs of a partial and a transitive dependency, removing a repeating group, resolving a many-to-many with a link table, derived values, and why the work is done on paper first.Open →
- Entity relationship modellingEntity relationship diagram, three degrees of relationship and optionality in a relationship.Open →
- Query languages and SQLPurpose of a query language, danger of an UPDATE or DELETE with no WHERE clause and three SQL aggregate functions and say what each returns.Open →
- Validation, verification and the DBMSRange check, data that passes every validation check and is still wrong and check digit.Open →
- Big Data, data warehousing and miningBig Data, data warehouse and data mining.Open →
- Distributed systems and distributed databasesDistributed system, distributed processing and distributed database.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Where does data at very large scale come from, why do relational databases struggle with it, and what is a warehouse for?
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What does data consistency mean, how does duplication threaten it, and what anomaly can result?
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Define a primary key.
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How does an entity in a model relate to a table in the implemented database?
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Why is a declarative query language preferable to writing retrieval code?
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Why can validation never guarantee correctness?
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What is a distributed system?
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What is data consistency?
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Define a foreign key.
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State the mantra summarising third normal form.
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What is an attribute?
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Write an SQL statement listing every column of the Student table.
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What is a range check?
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What is Big Data?
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What two things can be distributed in a distributed system?
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What is data redundancy?
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What goes wrong in a database where referential integrity is not enforced?
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A table holds OrderID, ProductID, Quantity, ProductName and ProductPrice, keyed on OrderID and ProductID. Which normal form does it fail?
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What is an entity relationship diagram?
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Write an SQL statement listing the names of students in Year 13.
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Which validation checks can the database enforce itself rather than a program?
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Name the three characteristics conventionally used to describe Big Data.
Key term
What is a distributed database?
Take Databases and Distributed Systems further
The same content, four other ways.
Questions from this topic
Each one with the model answer underneath.
- 1
What is data consistency?
Model answer
The property that a fact held in a database agrees with itself wherever it appears, so no two records contradict each other.
- 2
What is data redundancy?
Model answer
The unnecessary duplication of the same data in more than one place in a system.
- 3
Why is redundancy the underlying cause of inconsistency?
Model answer
If a fact is stored twice, an update that reaches one copy and not the other leaves the two disagreeing.
- 4
Give an example of an update anomaly.
Model answer
A customer's address stored on every one of their orders: changing it on one order leaves the older orders showing the previous address.
- 5
What is an insertion anomaly?
Model answer
Being unable to record one fact because another, unrelated fact is not yet known — a course cannot be stored until a student enrols on it.
- 6
What is a deletion anomaly?
Model answer
Losing one fact as a side effect of deleting another — removing the last student on a course deletes the course's details with them.
What is inside Levo
Six ways to work the same material.
Databases and Distributed Systems revision questions
- What does Databases and Distributed Systems cover in WJEC A-Level Computer Science?
- 8 subtopics: consistency, redundancy and data independence, relational organisation and normalisation, restructuring data into third normal form, entity relationship modelling, query languages and sql, validation, verification and the dbms, big data, data warehousing and mining and distributed systems and distributed databases. Each one has its own page with questions and model answers.
- How is Databases and Distributed Systems organised?
- By the WJEC 601-5345-3 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Databases and Distributed Systems, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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