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Trading Example: Video on Demand

Description

The Video on Demand example demonstrates of how to use the basic features of Trading Service. Features which are covered include:

• adding service type
• exporting and removing offers of services
• querying the Trading Service for service offers which meet specified requirements
• exporting proxy offers of service to the Trading Service

The Video-On-Demand example consists of:

• a set of servers (called Video Machines) which provide video feeds
• clients (called Television Sets)which receive video feeds

Video feed providers use the Trading Service to advertise their services to potential clients: clients use the Trading Service to locate the (previously advertised) video feeds that they want. A TV Company defines the types of service that the video feed providers can offer.

The following diagram shows the Video-on-Demand's architecture:

Source Files

The source files for the Video on Demand example are:

Video.idl - the IDL interface for the video feed objects. A Programme interface defines an attribute "title" and a show operation. The Film and SportsEvent interfaces both extend the Programme interface. The Film interface adds the attribute certificate"; the SportsEvent interface adds the attribute "sport".

TradingUtil.java - provides methods that resolve the Trading Service and obtain references to some of the components of the Trading Service. The class' methods are:

• getLookup is a static method that returns a reference to the Lookup component of the Trading Service.
• getRegister is a static method that returns a reference to the Register component of the Trading Service.
• getTypeRepos is a static method that returns a reference to the ServiceTypeRepository component of the Trading Service.
• getAdmin is a static method that returns a reference to the Admin component of the Trading Service.
• getProxy is a static method that returns a reference to the Proxy component of the Trading Service.

FilmImpl.java - implements the Film interface in Video.idl. The methods of this class are:

• The constructor creates a FilmImpl object giving details of its title, certificate, and the VideoMachine that can show it.
• certificate returns the certificate of the film.
• title returns the title of the film.
• show would broadcast the film but in this example the method just prints a message.
• description returns the combination of the title and the certificate.

SportsEventImpl.java - implements the SportsEventImpl interface from Video.idl. The methods of this class are:

• The constructor creates a SportsEventImpl object giving details of its title, sport, and the VideoMachine that can show it.
• sport returns the sport for the event.
• title returns the title of the event.
• show would broadcast the event but in this example the method just prints a message.
• description returns the combination of the title and the sport.

VideoMachine.java - a server that supplies video feeds. Its methods are:

• main creates a new instance of a VideoMachine object.
• constructor randomly chooses a number of television programmes for which it can provide video feeds, and then calls the export method to export offers of these video feeds. Finally, the constructor calls ObjectAdapter.ready() to establish the VideoMachine as a server.
• export exports a number of offers of video feeds to the Trading Service.
• withdraw withdraws all the previously exported offers of video feeds from the Trading Service.

TVCompany.java - adds the service types to the Trading Service. Is methods are:

• main creates a new TVCompany instance.
• The constructor obtains a reference to the Service Type Repository and then calls its add_type method to add the service types to the trader. The service types that are added to the trader are IDL:Video/Programme:1.0, IDL:Video/Film:1.0, and IDL:Video/SportsEvent:1.0.

TVSet.java - represents a television set that can request a video feed. Its methods are:

• main creates a new instance of the TVSet object.
• The constructor randomly chooses a programme. It then calls the query method to obtain an offer of a video feed of that programme. The show method of the Programme is called when a offer of service is obtained.
• query creates and performs a query to ask the trader where to obtain a video feed of the specified programme.

ProgrammeFactory.java - a server that can provide video feeds which are identical to those provided by the VideoMachine class above, except that the video feeds are not created until they are required. This class is a Lookup object. Its methods are:

• main creates a new instance of the ProgrammeFactory object.
• The constructor exports itself to the Trading Service as a proxy offer with the service type "programme".
• query is called by the Trading Service when a client requests a programme object. The constraint string is looked at to decide which programme the client requires. A new video feed is then created dynamically for the requested programme.

All other methods of this class are provided so that the class conforms to the Lookup interface; they are not used in the manipulation of the proxy offer.

How To Run This Example

If using an ORB which requires persistent POAs to be registered before they can be activated, ensure that that the OpenFusion.TradingTVCompany, OpenFusion.TradingVideoMachine, and OpenFusion.TradingTVSet POAs are registered.

1. Start the Trading Service from the command line or by using the Administration Manager.

   From the command line use:

   server -start TradingService

   Using the Administration Manager:

   Start the Administration Manager, right click on the TradingService node and select Start from the pop-up menu.

2. After starting the Trading Service, the TVCompany should be started first to add the service types to the Trading Service:

   run com.prismt.cos.CosTrading.examples.Video.TVCompany

3. Start one or more VideoMachines to export offers of video feeds to the Trading Service:

   run com.prismt.cos.CosTrading.examples.Video.VideoMachine

4. Finally, in a new window, TVSets are used to request video feeds. (some programmes may not be available, depending on whether they were exported to the Trading Service in step 2):

   run com.prismt.cos.CosTrading.examples.Video.TVSet

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