What does syntax analysis check?

It checks that the stream of tokens forms statements that obey the grammatical rules of the language.

Parsing is the process of working out how a sequence of tokens fits the rules of the language, and building a structure that records how the statement is put together.

What does syntax analysis pass on to the next stage?

It passes on a structured representation of the program showing how its statements and expressions are nested, rather than the flat sequence of tokens it received.

Why does a translator normally continue after finding the first syntax error?

So the programmer can be given a list of all the faults it can detect in one run, instead of having to retranslate after correcting each one.

Why can one genuine mistake produce several error messages?

The analyser loses track of the structure at the point of the fault, so the statements that follow no longer fit the rules until it manages to resynchronise.

WJEC A-Level Computer Science 601-5345-3

Hardware: Architecture, Memory and Storage

Topic overview Components of a computer system and how they connect Von Neumann architecture and the CPU The fetch-execute cycle Memory and caching Parallel processing Input and output devices and their uses Secondary storage, fragmentation and defragmentation

Networks and Data Transmission

Topic overview Serial and parallel transmission Simplex, half duplex and full duplex Multiplexing and switching Packets and the TCP/IP protocol stack Networks, standards and protocols Collisions and shared media Routing, addressing and the internet

Logic Gates and Boolean Algebra

Topic overview Logic gates and their truth tables Boolean notation and expressions Building and reading truth tables Boolean identities and rules Simplifying Boolean expressions De Morgan's laws Masking and clearing registers

Data Representation and Data Types

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Data Structures

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Organisation of Data: Files and Records

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Database Systems

Topic overview Flat files and the relational model Relational and other contemporary database systems Primary, foreign, composite and candidate keys Indexes and links between tables Entity relationship modelling Normalisation to third normal form The database management system, queries and user views

The Operating System

Topic overview The need for an operating system The kernel and process management Memory protection and the backing store The user interface between user and hardware Directory structures and file attributes Utility software Batch, real time control and transaction processing

Algorithms and Programs

Topic overview Defining and designing algorithms Variables, constants and identifiers Scope, subprograms and parameter passing Sequence, selection and repetition Mathematical and logical operations Standard algorithms: sorting, searching and compression Dry running, trace tables and test data

Principles of Programming

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Systems Analysis

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Software Engineering and Program Construction

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Types of Software System

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Practical Programming

Topic overview Designing data structures: fields, records and data types Key fields and methods of access Validation of input data Designing routines with pseudocode Tracing code and test data Prototyping and evaluating a solution Annotated listings and readable code

Data Security and Integrity

Topic overview Dangers of holding files of personal data Levels of permitted access and access control Passwords and authentication Clerical procedures and write-protection Threats to computer systems Malicious and accidental damage to data Contingency planning and disaster recovery

Computing, Society and the Law

Topic overview Social and economic change from computing Computers and the nature of employment The digital divide and cultural change Environmental cost of computing Data protection and freedom of information law The Computer Misuse Act 1990 and computer crime Copyright, surveillance and professional codes

Advanced Data Structures and Logic

Topic overview Arrays in three dimensions Stacks and queues using pointers and arrays Linked lists using pointers and arrays Binary trees using pointers and arrays Hash tables and collision resolution NAND, NOR and Boolean simplification Masking, clearing registers and encryption

Recursion, Sorting and Searching

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Programming Paradigms and Translators

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System Design and Human-Computer Interaction

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Software Engineering Tools and Professional Practice

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Advanced Architecture and Assembly Language

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Communication Networks and File Organisation

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Number Representation and Floating Point

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Databases and Distributed Systems

Topic overview 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 Distributed systems and distributed databases

Operating System Management

Topic overview Types of operating system Interrupts and interrupt handling Memory management and partitioning Buffering and data transfer Scheduling and process states Scheduling policies and priorities Evaluating operating system design

Software Systems and Applications

Topic overview The range of software system types Safety related and safety critical systems Computer control and automation The scope of automation in practice Expert systems The internet, intranets and search Selecting and evaluating a software system

Data Security, Cryptography and Attack

Topic overview Integrity problems in online updating The need for cryptography Symmetric and asymmetric techniques Classical ciphers and cryptographic algorithms Comparing cryptographic strength Biometric technologies Malicious software and its vectors Attacks, defence and penetration testing

Software Engineering and Program Construction

Syntax and semantic analysis

3 things to know
AS Unit 1

Overview

Faults that syntax analysis would report and type error found by semantic analysis.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain why checking types before the program runs is safer than checking them as it runs.

Key term

Give two examples of faults that syntax analysis would report.

Key term

What is parsing?

Questions from this subtopic

Each one with the model answer underneath.

1
What does syntax analysis check?
Model answer
It checks that the stream of tokens forms statements that obey the grammatical rules of the language.
2
Give two examples of faults that syntax analysis would report.
Model answer
A selection statement left without its closing keyword, and an arithmetic expression with an operator but no second operand.
3
What is parsing?
Model answer
Parsing is the process of working out how a sequence of tokens fits the rules of the language, and building a structure that records how the statement is put together.
4
What does syntax analysis pass on to the next stage?
Model answer
It passes on a structured representation of the program showing how its statements and expressions are nested, rather than the flat sequence of tokens it received.
5
Why does a translator normally continue after finding the first syntax error?
Model answer
So the programmer can be given a list of all the faults it can detect in one run, instead of having to retranslate after correcting each one.
6
Why can one genuine mistake produce several error messages?
Model answer
The analyser loses track of the structure at the point of the fault, so the statements that follow no longer fit the rules until it manages to resynchronise.

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