Domain-Driven-Design Based Design And Realization Of The Software For Booking Office Machine In Rail Transit

Automated Fare Collection (AFC) system plays a very important role in the area of railtransit of an international metropolis. It serves to automate the whole process of ticketing,validating, billing, fare collecting and statistics. It consists of four ties as central clearinghouse, station computers, terminal devices and fare media. The terminal devices of AFCinclude entry/exit fare gate, ticket vending machine, booking office machine, card vendingmachine, ticket handling machine, etc. The Booking Office Machine (BOM) is an essentialpart of AFC system. It is a complete set of station ticketing process system that providesticket vending, ticket analyze, card recharge, card renew, inquiry, updating, excess farecharging, operation display, etc. The BOM of Shanghai rail transit has been domestictransformed for about ten years. The business module and technique framework of itssoftware architecture are highly tight coupled and the design of its modules is base onprocedure-oriented, which turns out to be a barrier for the further development of its software.With the development of the business of Shanghai metro, mutiple new fare media serviceshave been released. The business rule becomes more complicated and is changed frequently.Apart from that, the market of AFC also keeps extending from metro to other areas such asintercity railway. As a result, how to design a loose coupling structure and separate thedifferent concerns of domain and technique in development of BOM in order to provideenough extensiblities and maintensiblilty has become a pending problem.Against the problems listed above, this article takes a real project as its background todesign and realize a Model-Driven Design based proto type of BOM by leveragingDomain-Driven Design. The test result shows that this proto type is feasible and effective.Compared with other similar software, the work of this article has a few differentcharacteristics as belowed:1) Combined the use of domain model with layed architecture design, it isolates thedomain-related modules into a domain layer which gets rid of the dependencies on technical framework. This meets the requirement that the domain models need to be reused in differentapplication environments.2) The communication module has been designed with a custom protocol serializationframework following the standard of industry, which makes the universalitis significantlyincreased.3) The design and realization of the business modules meets the requirement ofmanagement of massive ticketing business rules, which can subscribe and perform processrules, make ticketing process rules independent to each other and provide rules with thecharacteristic of plugin corresponding to the kind of the ticket being dealt.4) By using Behavior-Driven-Development methodology and supported tools, itaccommodates the software specification for development through the features defined innature language in project and also can be transformed into User Acceptance Test (UAT) tovalidate the behaviors of software are as expected.The BOM designed in this article is under validation in a test enviroment. And theprevious version of it is running normally with stable performance in serveral Shanghai metrolines till now.