Jet Retail General

Structure of the system

In the real world Jet Retail application will be used to implement critical business systems. The application developer must be able to deal with the challenges presented by multi-user distributed system architectures that are prevalent today. Maintaining data integrity in these environments is of utmost importance. It was decided that the structure of the application should provide the tools required to manage critical information in the most effective way--in an object-oriented way.

Application Architecture

The figure (below) illustrates the architecture of Jet Retail application

Looking across these architectures the first thing to notice is the flexibility of the Business Object Engine (BOE). The BOE provides all the core services of the data access tier in a Data Access application. It provides the object-relational translation as well as encapsulation of the data source. The BOE can be native Delphi component or an ActiveX component. If it is an Active X component it can be located on a client machine (Client A architecture) or on a server machine (Client B and C architectures). Management of information between the database and the BOE and the BOE and your application

The successful implementation of an object-relational system includes a solution for two complex problems; management of real data to and from the data store(s) and management of the task of converting data to and from objects.

Main advantages of this realization

• Isolated database server, which means a possibility to work with different type of servers. This will needs changes only in business object engine
• Different solutions for client application:
• Client A with normal workstation
• Client B with thin client PC. We started a research for a possibility to develop Embedded PC with Windows CE, which can work as POS terminal (Cash Register)
• Client C with WEB based application. In case of OeAMTC this is possible solution for centralized data maintenance

Possible problems during the implementation

• The architecture with capsulated database is more sensitive to the wrong database design
• The system cannot rely on build in error handling in database server. Complex error handling mechanism has to be implemented
• To develop needed set of business objects needs time and visible result of the development come later then using direct implementation.
• It seems to be more difficult to tune the system, because the performance depends of different layer

Jet Retail / OeAMTC

Short description

The project aim is to equip the checkpoints at Austrian borders of OAMTC with a new software. The software shall be developed according to the special requirements of the border-checkpoints. It shall support following functions:

Front Office

• Currency exchange
• VAT refunding
• Credit card cash withdrawals and check disbursements
• Motorway vignette sales
• Product sales

Back Office

• Currencies and exchange rates management
• Global Refund import/export functionality
• Stock control
• User management
• Specific implementation of Day Start/ Day End
• Import export functionality

Development platform

To develop the systems Oracle server 7.3 and Delphi 4 were chosen as development platform. Some of the reasons were:

• Oracle licenses are available in OAMTC
• Oracle has a very good enhanced SQL language
• Delphi offers capability to quickly develop reliable database applications
• Jet Systems has enough experienced Delphi programmers

Business objects overview.

Goals.

The purpose was to create a system (library) of classes, called business objects. They comprise the business logic and functionality. As a rule, one business object presents some real object (term) of the considered area (i.e. TGood is managing the information for specified good--its characteristics, actual price in chosen currency and so on). There are also classes, which are managing some operations (various kinds of front office transactions for example) and a base class, which is ancestor of all business objects and encapsulates.

Benefits.

• Clear and stable model. The business objects ease the understanding of the whole system, because they employ the object-oriented technology. So it raises the system's stability, extendibility and eases the business logic changes when necessary. For example the TCommission object is maintaining not only commission editing and storage in the database, but also it calculates a commission value, based on given amount. It also is tracking if that amount is within the specified range of appliance of the commission.
• Capsulation. Business objects are maintaining its storage in the database itself. So when some changes are made in the database schema, then only the appropriate object should be changed accordingly. The calculations and business checks are capsulated in the objects (see the example above).
• Inheritance. Reusability of code by implementing the common behavior and properties in some classes and then just inheriting them to reuse. For example all the association logic and maintaining event handling of the objects are declared and implemented in the base class THolder.
• Reusability. Most of the objects can be reused in various UI forms and each other. For example the TMedia object is used in the back office form for editing specified media and inserting new one, but also in many other classes like TExchange, TPOSSale and so on. Additionally, most of the objects can be reused in other projects with minor modifications.

Description of the application structure

Lowest level is the database server, which in this case is Oracle 7.3.

Business objects part actually consists of 3 layers:

Data access Services

Before the application can interact with objects created from the RDBMS by the Business Object Engine it must connect to all the required data sources. The application can interact with one or more data sources. The application must connect to the data sources it wishes to use prior to issuing database queries, loads, stores, etc.

Data access services provide the interface to connect with data sources.

Business Object Services

A business object is an instance of a class that is mapped to the database. Business objects provide the object-oriented view of your database.

User interface objects

User interface objects contain all the functionality to interact with the user and with business objects. They map the forms and dialogs to the business objects and transfer (translate) the information from human understandable presentation to object presentation and from the object to the operator

Jet Systems Sofia, Bulgaria phone: +359-2-975-3750