CHAPTER 3:  BASIC ACCENT R OBJECTS

This chapter introduces all the elements that comprise ACCENT R, and describes their relationships to one another.

ACCENT R uses an application repository called a Data Base Library (DBL).  The DBL serves both as an actively maintained data dictionary and a central storage area for the entire application.  The DBL provides information about how each DBL object is structured, processed, and related.

The DBL structures the modern Computer Aided Software Engineering (CASE) oriented design, development, implementation, and maintenance of applications.  The DBL is the common interface between the 4th Generation Structured Programming Language (SPL), the 4th Generation Tools, and the Open Structured Query Language (OSQL) database structure.

The object orientation of the DBL insulates the programmer from the internal workings of the individual modules and routines of the application.  The developer does not have to know about the inner workings of the object and thus can concentrate on the more important concept of what to do with the results or actions of the object.  Another benefit of the object orientation of the DBL is that the object can be changed without the programmer having to re-design and re-code the entire application.  This separation and reusability of the DBL objects provides greater productivity than a traditional Third Generation Language (3GL) and screen-driven-only Fourth Generation Languages (4GL's).  Consequently, the developer tells ACCENT R what the application should do, and not specifically how to do it.

DBL objects can be grouped into two categories:  General Purpose (used in most applications) and Ancillary Purpose which offer special capabilities for problem solving not possible in other 3GL's or 4GL's.

The Data Base Library (DBL) is discussed first with an overview of the other objects.  A comprehensive view of Schema Definitions (SD’s), Data Sets (DS’s), and Data Indexes (DI’s) is given next.  The programming objects are presented briefly here to make their relationship to the overall framework clear.  Volume II of this Manual is devoted to the in-depth discussion of the programming objects.

NOTES:  A data base administrator is not required to oversee the ACCENT R data base system.  Each user has the ability to access DBL objects.  Access to DBL objects can be restricted with the Security module.  The Security module is an optional utility which is described in a separate manual called ACCENT R Security.  We strongly recommend, for large applications, that a data base administrator be assigned to the implementation team.

General Purpose DBL Objects

DATA BASE LIBRARIES

The Data Base Library (DBL) is the primary object of ACCENT R in that it contains the definitions for all other objects.  Unlike some data dictionaries that offer only passive control, the DBL is an actively maintained file that serves as a user control point for the entire data base.

The DBL is a System File (SF) with the default extension .DBL.  ACCENT R is designed so that all files and other objects that relate to a given application can be controlled through a single DBL.  It is possible to combine several applications in one DBL, or to split parts of an application between two or more DBL’s, but as a general rule it is most efficient to use the principle of "one application per DBL." Many DBL’s can be stored in one directory, or a directory can be limited to one DBL.

As the central organizational unit, the DBL contains all application logic and processing procedures Command Modules (CM) and Process Modules (PM), all descriptions of the records in the data base Schema Definitions (SD), and the locations of the information Data Sets (DS), as well as the entry point to all these objects.  The DBL also contains the definitions of shared activity data called Global Storage (GS).  It can contain the names of all SF’s related to the application.  Through the DBL, ACCENT R controls and maintains important information about the data base, as well as all related application programs.  By maintaining in a single DBL file all information for a given application or data base, ACCENT R provides not only a complete information source but control and security protection as well.

In addition, ACCENT R provides cross-DBL capabilities, allowing commands and programs to access objects in DBL’s other than the current one.  To access an object in another DBL, simply specify the DBL name after the object name, such as:

object_name IN DBL dbl_name

The IN DBL clause is described in a later chapter.  Without the IN DBL clause, an object is normally assumed to exist in the current DBL.  When executing a CM, ACCENT R assumes that object references (without the IN DBL clause) exist within the DBL from which the CM is executed.

Figure 3-1, shows how each of the objects of ACCENT R relates to the DBL and to other objects that are used for the same application.  The DBL is the primary organizational unit of an ACCENT R application.  It is a SF that catalogs names and other directory information for all ACCENT R objects that make up an application.  Some of the objects are stored completely within the DBL file, while others exist as separate SF’s, but are associated with the application through entries in the DBL.

To view a diagram of this click here: Figure 3-1 The Data Base Library in Relation to Other ACCENT R Objects.

The following is a brief paragraph introducing each of the ACCENT R objects and refers to places in the manual that offer comprehensive discussions and related information about each one.

Schema Definitions

A Schema Definition (SD) describes the fields and records in a Data Set (DS), and must be defined before the associated DS can be created.  The DEFINE SD command which invokes the ACCENT R editor, is used to define the SD.  SDs track maximum record lengths for flexibility.

Data Sets

After a Schema Definition (SD) has been defined, the associated Data Set (DS) is created by the CREATE DS command.  The Data Base Library (DBL) entry for each DS contains the name of its SD.  Data is put into a DS with the ENTER command, LOAD command or OSQL INSERT.  All of the Data Manipulation Commands operate on the data in DS’s.

Data Indexes

For Data Sets (DS) of any substantial size, a Data Index (DI) can greatly increase the efficiency of retrieval and data manipulation.  The Data Base Library (DBL) entry for a DI identifies the DS and Schema Definition (SD).  A DI is defined with the DEFINE DI command which calls up the ACCENT R edit environment.

Index Definitions

An Index Definition (ID) defines a general index definition for a Schema Definition (SD), which can then be used to create Data Indexes (DI) for any Data Set (DS) associated with the SD.  An ID is defined with the DEFINE ID command.  The statements that make up an ID are similar to those of the DI definitions.

Control File

A Control File (CF) is associated with a single Data Set (DS).  The CF coordinates access to the associated DS during Simultaneous Update.

Process Modules

The primary programming object of ACCENT R is the Process Module (PM).  ACCENT R provides a model structure, which a can easily be tailored to any data processing situation by the choice of PM statements.  To create a PM, use the DEFINE PM command.

Command Modules

The Command Module (CM), which can contain almost any of the commands that are used interactively, is generally used to invoke one or more PMs, and to tie together the individual programs and data fields that represent a data processing unit.  To create a CM, we the DEFINE CM command.

Global Storage Definitions

Global Storage (GS) definitions provide an area for temporary storage of data to be accessed by more than one program.  Up to 10 GS definitions can be active in session.  Use the DEFINE GS command to create a GS.

System Files

Any System File (SF) can be cataloged in a Data Base Library (DBL), whether created within the ACCENT R environment or not.  This facility is usually used to identify any log files, startup files, or report files which are part of the application.

Find Subset

A subset of records that has a separate index and can be manipulated as a distinct unit from the rest of the records in the same Data Set (DS).  Though designed to be temporary, Find Subsets (FS) can be saved from one session to another.  FSs are created and accessed through the record retrieval commands.

System Information

A System Information (SI) allows an application to be documented on line, in the applicable Data Base Library (DBL), rather than in a separate disk file or hard-copy document.  Such information as the names and functions of Data Sets (DS), Data Indexes (DI), Command Modules (CM), and Process Modules (PM) that make up an application can be stored together in one SI.  In short, any information that needs to be stored can be kept in an SI.  An SI is defined with the DEFINE SI command and modified through the MODIFY SI command.  The number of SI’s that can be stored in one DBL is limited only by system resources.

Code Segment

Code Segments (CS) stores commonly used statements which can be added to a DBL object at compilation using the INCLUDE statement.  There is no syntax checking when a CS is defined.  There may be several separate segments within one CS.  Arguments may be placed in a CS with their values specified when the segment is INCLUDED.  They can be created by the DEFINE CS command.

Object Interaction and Subordination

An object-oriented approach to application development is one in which objects or modules of the application are selected and built in a goal-directed fashion.  The table below shows each object has a specific purpose.  Each Data Base Library (DBL) object represents a particular type of application building block.  Objects can be associated with one another in a modular fashion.  It is not necessary for the developer to know about all the internal workings of an object to use it in building an application.  An understanding of how DBL objects subordinate to each other is an essential element in applying ACCENT R to application development in a goal-directed style.

 

OBJECT ID	OBJECT NAME	OBJECT PURPOSE
CF	Control File	Control Simultaneous Update
CM	Command Module	Interactive Command Language Statements
CS	Code Segment	Reusable Code
DBL	Data Base Library	The Central Application Repository
DI	Data Index	Index Definition
DS	Data Set	Table on file containing the actual data
FS	Find Subset	Pointer File for Subsets of data
GS	Global Storage	Shared Memory Variables
ID	Index Definition	General Index Definition
PM	Process Module	Structured Programming Language Statements
SD	Schema Definition	Records or Row Definitions
SF	System File	System Level Files
SI	System Information	Free Format Text for application documentation

Table 3-2 DBL Objects