4G LANGUAGE :
An Introduction…
Dr. Mohammad Iqbal
Source : www.wittyengineers.com
Programming Language
• A programming language is a machine-readable artificial
language designed to express computations that can be
performed by a machine, particularly a computer.
• Programming languages can be used to create programs that
specify the behavior of a machine,to express algorithms.
• Many programming languages have their syntax and
semantics.
Generations of Programming
Language
• 1st Generation: (1950-60) machine language.
• 2nd Generation: (1961-75) assembly language.
• 3rd Generation: (1976-92) high-level programming languages,
such as C, C++, and Java.
• 4th Generation: (1993-2005) typical high-level programming
languages closer to human languages.
• 5th Generation: (2005-..) used for artificial intelligence and
neural networks.
First-generation programming
language
• A first-generation programming language is a machine-level
programming language.
• No translator was used to compile or assemble the firstgeneration language.
• The main benefit of first-generation programming language is
that the code a user writes can run very fast and efficiently.
• It is a lot more difficult to learn than higher generational
programming languages, and it is far more difficult to edit if
errors occur.
• Machine language is an example of 1st G Language.
• Sometimes referred to as machine code or object code.
• It is a collection of binary digits or bits that the computer reads
and interprets.
Second-generation programming
language
• Second-generation programming language is a generational
way to categorize assembly languages.
• Second-generation programming languages have the following
properties:
• The code can be read and written by a programmer. To run on a
computer it must be converted into a machine readable form, a
process called assembly.
• The language is specific to a particular processor family and
environment.
Assembly language
• It is an example of 2nd G Language.
• Assembly languages are a family of low-level languages
for programming computers.
• It implements a symbolic representation of the numeric
machine codes.
• Other constants needed to program a particular CPU
architecture.
Assembly language
Assembler
• Assembler creates object code by translating assembly
instruction mnemonics into opcodes, and by resolving
symbolic names for memory locations and other entities.
• Assemblers are generally simpler to write than compilers
for high-level languages.
Third-generation programming
language
• The introduction of the compiler in 1952 spurred the
development of third-generation computer languages.
• These languages enable a programmer to create program
files using commands that are similar to spoken English.
• Third-level computer languages have become the major
means of communication between the digital computer and
its user.
• Such as BASIC, C, FORTAN and Pascal.
Third-generation programming
language
High-level language
• 3rd G Languages are High-level Languages.
• After a program is written in one of the high-level languages, it must be
either compiled or interpreted.
Third-generation programming
language
• A Compiler program rewrites the program into machine
language that the CPU can understand. This is done all
at once and the program is saved in this new form.
• A compiled program is generally considerably larger than
the original.
• An Interpreter program translates the program
statements into machine language one line at a time as
the program is running.
• An interpreted program will be smaller than a compiled
one but will take longer to execute.
Fourth-generation programming
language
• A fourth-generation programming language (1970s1990) (abbreviated 4GL) is a programming language or
programming environment designed with a specific
purpose in mind, such as the development of
commercial business software.
• In the evolution of computing, the 4GL followed the 3GL
in an upward trend toward higher abstraction and
statement power.
• The 4GL was followed by efforts to define and use a
5GL.
Fourth-generation programming
language
• 3GL development methods can be slow and error-prone.
• Some applications could be developed more rapidly by
adding a higher-level programming language and
methodology which would generate the equivalent of
very complicated 3GL instructions with fewer errors.
• All 4GLs are designed to reduce :
 programming effort,
 the time it takes to develop software and
 the cost of software development.
Fourth-generation programming
language
• Fourth-generation languages have often been compared
to domain-specific programming languages (DSLs).
• For example, a typical 4GL command is
FIND ALL RECORDS WHERE NAME IS "SMITH"
Types of 4 GL :• Table-driven (codeless) programming, usually running
with runtime framework and libraries. Instead of using code.
• Report generators take a description of the data format
and the report to generate and from that they either
generate the required report directly or they generate a
program to generate the report.
• Data management 4GLs such as SAS, SPSS and Stata
provide sophisticated coding commands for data
manipulation, file reshaping, case selection and data
documentation in the preparation of data for statistical
analysis and reporting.
Some fourth-generation
languages
•
•
•
•
•
•
•
•
FoxPro
PowerBuilder
SQL
Report Builder
Oracle Reports
Graph Talk
MATLAB
CSS
Examples of 4G Languages
FoxPro
FoxPro has two meanings:
• Visual FoxPro - an object-oriented programming
language and RDBMS, published by Microsoft, for
Microsoft Windows.
• FoxPro 2 - a text-based procedural programming
language and RDBMS, originally published by Fox
Software and later by Microsoft, for MS-DOS, Microsoft
Windows, Macintosh, and UNIX
Examples of 4G Languages
Database query languages
• Query languages are computer languages used to
make queries into databases and information
systems.
• Query languages can be classified according to
whether they are database query languages or
information retrieval query languages.
• SQL is a well known query language for relational
databases.
• XQuery is a query language for XML data sources.
Fifth-generation programming
language
• Fifth generation computing devices, based on artificial
intelligence, are still in development, though there are
some applications, such as voice recognition, that are
being used today.
• The use of parallel processing and superconductors is
helping to make artificial intelligence a reality.
• The goal of fifth-generation computing is to develop
devices that respond to natural language input and are
capable of learning and self-organization.
Fifth-generation programming
language
Examples :
Artificial intelligence :
• The branch of computer science concerned with making
computers behave like humans.
• There are several programming languages that are
known as AI languages because they are used almost
exclusively for AI applications. The two most common
are LISP and Prolog.
Fifth-generation programming
language
Examples :
Neural network
• A type of artificial intelligence that attempts to imitate the way a
human brain works.
• A neural network works by creating connections between
processing elements, the computer equivalent of neurons.
• Neural networks are currently used prominently in voice recognition
systems, image recognition systems, industrial robotics, medical
imaging, data mining and aerospace applications.
4th Generation Programming
Languages
• A fourth-generation programming language (or 4GL)
is a programming language designed with a specific
purpose in mind such as the development of commercial
business software.
• fourth-generation languages are closer to human
languages than typical high-level programming
languages.
• Most 4GLs are used to access databases.
History Of 4GL
• The term 4GL was according to James Martin first used in his
1982 book Applications Development Without Programmers to
refer to non-procedural high-level specification languages.
– A SPECIFICATION language is one that enables a
programming task to be performed by the construction of a set
of non-procedural statements.
• In 1987 Grindley distinguished between a Pure and a
HYBRID 4GL
Why 4GL?
• Programming effort
– They can be easily learnt since there are relatively
few commands, functions and structures.
•
•
•
•
The cost of software development.
Alter and maintain
Ease of use
Simplicity of design and implement
Why 4GL?
• The time it takes to develop software
– Programs written in a 4GL can be written very quickly. Each
statement written may generate a large amount of code containing a
high level of functionality and productivity. For example, consider
the SQL statement:
SELECT surname, line_no, ddress_line
FROM patient, patient_address
WHERE patient.nhs_no=patient_address.nhs_n
ORDER BY patient.nhs_no, line_no
To write the equivalent in a 3GL would require many lines of code
and the procedural and iteration structures that are absent from SQL.
Different Types Of 4GL
– Theory
• Pure 4GL: A specification language made up of non-procedural
instruction sets.
• HYBRID 4GL: A number of pure 4GLs combined with and held
together by a more procedural language.
– Implementation
• Report generators
• Forms generators
• 4GLs (sometimes termed fourth generation environments)
– attempt to automatically generate whole systems from the outputs
of CASE tools, specifications of screens and reports, and possibly
also the specification of some additional processing logic.
Additional Components
• Some 4GLs have integrated tools which allow for the easy
specification of all the required information.
– James Martin's Information Engineering systems development
methodology
• allow the input of the results of system analysis and design in the form of Data Flow
Diagrams, Entity Relationship Diagrams, Entity Life History Diagrams etc from
which hundreds of thousands of lines of COBOL would be generated.
– Oracle Corporation’s Oracle Designer and Oracle Developer
• could be integrated to produce database definitions and the forms and reports
programs.
4GL Advantages & Disadvantages
• Being specification languages, their use requires,
in theory at least, no programming task; the
necessary code will be generated directly from
the specification.
• Can only address a small and very highly
specialized area of development
4GL In Action
• Database query languages:
– SQL
– Oracle SQL*Plus
– Progress 4GL
• Data-stream languages:
– AVS
– APE
– Iris Explorer
• Screen painters and generators:
– Oracle Forms
4GL In Action
• Report Generators:
– Oracle Reports
– LINC
– GEMBase
– BuildProfessional
– Informix-4GL
– Focus
– Metafont
– RPG-II
– S
– IDL-PV/WAVE
– Gauss
– Mathematica
Oracle
As A 4GE
FOURTH GENERATION
ENVIRONMENT (4GE) ?
• In order to provide an environment in which a
complex system can be developed, a number of
different types of "pure" fourth generation
languages must be integrated, and further
procedural programming facilities must be
provided.
4GE Components
Typical 4GE components:
– END-USER QUERY LANGUAGE (e.g. SQL),
– SCREEN FORMATTER (e.g. Oracle's screen painter in
SQL*Forms),
– REPORT GENERATOR.
4GE Components
• DATA DICTIONARY :
– Central to all fourth generation environments
– A system database, rather than a user database, which holds
metadata as opposed to the data itself and the DATABASE
MANAGEMENT SYSTEM.
– A place to store all the various schemas and mappings in both
source and object form
– Cross-reference information :
•
•
•
•
Which programs use which pieces of the database
Which user requires which reports
Qhat terminals are connected to the system
…
Page 15 Of 33
DBMS Rules
• The database management system performs two
functions:
– Filehandler for the systems developed using the
components of the 4GE
– It is the software that manages the data dictionary.
Page 16 Of 33
Oracle as a 4GE
– SQL*Plus Allows users to create and manipulate tables using SQL.
– SQL*Forms An interactive applications generator for creating advanced, forms-based
applications.
– SQL*Loader A module to simplify the process of the entry of large quantities of data
into tables.
– SQL*Report A module for generating complex reports.
– SQL*Menu A module to enable the coordination of forms by an interactive menuing
system.
– SQL*DD Design Dictionary - a structured system to monitor and control the
development from the initial analysis to running and maintenance.
– EASY*SQL An interface for inexperienced users of SQL using a mouse and screen
graphics.
– SQL*Calc An Excel compatible spreadsheet that may use database data; the spreadsheet
cells can call SQL statements.
– SQL*Graph Provides a graphical representation of data retrieved from the database.
– SQL*Text A module for creating a forms interface to large text databases.
Page 17 Of 33
SQL
Structured Query Language
Page 18 Of 33
SQL Command Types
Query Commands
– Select
– Create View
– …
• Update Commands
–
–
–
–
Insert
Delete
Update
…
Page 19 Of 33
Retrieving Data (Select Command)
• A typical SQL query has the form:
select A1, A2, ..., An
from r1, r2, ..., rm
where P
– Ais represent attributes
– ris represent relations
– P is a predicate.
• The result of an SQL query is a relation.
Page 20 Of 33
Retrieving Data (Views)
• Provide a mechanism to hide certain data from the view of certain
users. To create a view we use the command:
where:
 <query expression> is any legal expression
 The view name is represented by v
• A view consisting of branches and their customers
create view all-customer as
(select branch-name, customer-name
from depositor, account
where depositor.account-number = account.account-number)
union
(select branch-name, customer-name
from borrower, loan
where borrower.loan-number = loan.loan-number)
Page 21 Of 33
Modification of the Database
•
Delete all account records at the Perryridge branch
delete from account
where branch-name = ‘Perryridge’
•
Add a new tuple to account with balance set to null
insert into account
values (‘A-777’,‘Perryridge’, null)
•
Increase all accounts with balances over $10,000 by 6%, all other
accounts receive 5%.
update account
set balance = balance  1.06
where balance > 10000
Page 22 Of 33
Domain Types in SQL
•
•
•
•
•
•
•
•
•
char(n). Fixed length character string, with user-specified length n.
varchar(n). Variable length character strings, with user-specified maximum length n.
int. Integer (a finite subset of the integers that is machine-dependent).
smallint. Small integer (a machine-dependent subset of the integer domain type).
numeric(p,d). Fixed point number, with user-specified precision of p digits, with n
digits to the right of decimal point.
real, double precision. Floating point and double-precision floating point numbers,
with machine-dependent precision.
float(n). Floating point number, with user-specified precision of at least n digits.
Null values are allowed in all the domain types. Declaring an attribute to be not null
prohibits null values for that attribute.
create domain construct in SQL-92 creates user-defined domain types
create domain person-name char(20) not null
Page 23 Of 33
Date/Time Types in SQL (Cont.)
•
date. Dates, containing a (4 digit) year, month and date
– E.g. date ‘2001-7-27’
•
time. Time of day, in hours, minutes and seconds.
– E.g. time ’09:00:30’
•
time ’09:00:30.75’
timestamp: date plus time of day
– E.g. timestamp ‘2001-7-27 09:00:30.75’
•
Interval: period of time
– E.g. Interval ‘1’ day
– Subtracting a date/time/timestamp value from another gives an interval value
– Interval values can be added to date/time/timestamp values
•
Can extract values of individual fields from date/time/timestamp
– E.g. extract (year from r.starttime)
•
Can cast string types to date/time/timestamp
– E.g. cast <string-valued-expression> as date
Entity Management Commands
•
An SQL relation is defined using the create table command:
– create table branch
(branch-name
char(15) not null,
branch-city
char(30),
assets
integer)
•
The drop table command deletes all information about the dropped relation from the
database.
•
The alter table command is used to add attributes to an existing relation.
– alter table r add A D
•
The alter table command can also be used to drop attributes of a relation
– alter table r drop A
Page 25 Of 33
Embedded SQL
• The SQL standard defines embeddings of SQL in a variety of programming
languages such as Pascal, PL/I, Fortran, C, and Cobol.
• A language to which SQL queries are embedded is referred to as a host language,
and the SQL structures permitted in the host language comprise embedded SQL.
• EXEC SQL statement is used to identify embedded SQL request to the preprocessor
EXEC SQL <embedded SQL statement > END-EXEC
Note: this varies by language. E.g. the Java embedding uses
# SQL { …. } ;
Sample:
EXEC SQL
declare c cursor for
select customer-name, customer-city
from depositor, customer, account
where depositor.customer-name = customer.customer-name
and depositor account-number = account.account-number
and account.balance > :amount
END-EXEC
Dynamic SQL
• Allows programs to construct and submit SQL queries at run time.
• Example of the use of dynamic SQL from within a C program.
char * sqlprog = “update account
set balance = balance * 1.05
where account-number = ?”
EXEC SQL prepare dynprog from :sqlprog;
char account [10] = “A-101”;
EXEC SQL execute dynprog using :account;
• The dynamic SQL program contains a ?, which is a place holder for a value that
is provided when the SQL program is executed.
Microsoft English
Query
What Is English Query?
With English Query, developers can use their SQL
and OLAP databases as a basis to build an English
Query application, which allows end users to query
the database in English.
SELECT sum(Orders.Quantity) from Orders, Parts WHERE Orders.State='WA'
and
Datepart(Orders.Purchase_Date,'Year')='1996'
and
Part.PartName = 'ProductX' and Orders.Part_ID = Parts.Part_ID
How it works?
References
•
•
•
•
•
•
•
Microsoft English Query Tutorials
Microsoft SQL Server 2000 User Manual
http://portal.acm.org
http://burks.brighton.ac.uk/
http://www.soi.city.ac.uk/
http://en.wikipedia.org/wiki/4GL
http://encyclopedia.fablis.com/index.php/Fourth-generation_language
Descargar

Document