Towards requirements-driven information systems engineering: the Tropos project

Question

Towards requirements-driven information systems engineering: the Tropos project (answer the following questions)

1. Search and summarize what the TROPOS project is?

2. What are the key challenges of this effort?

3.How can the software development model address (good or poor) towards organizational model of actor and goal dependency?

4. Discuss the key considerations of this effort.

NOTE: Tropos explores multiple phases through an e-business example, and sketches a formal language which underlies the methodology and is intended to support formal analysis. The methodology seems to complement well proposals for agent-oriented programming platforms.

Explanation / Answer

1.Information systems have traditionally suffered from an impedance mismatch. Their operational environment is understood in terms of actors, responsibilities, objectives, tasks and resources, while the information system itself is conceived as a collection of (software) modules, entities (e.g., objects, agents), data structures and interfaces. This mismatch is one of the main factors for the poor quality of information systems, also the frequent failure of system development projects. One cause of this mismatch is that development methodologies have traditionally been inspired and driven by the programming paradigm of the day. This means that the concepts, methods and tools used during all phases of development were based on those offered by the pre-eminent programming paradigm. So, during the era of structured programming, structured analysis and design techniques were proposed , while object-oriented programming has given rise more recently to object-oriented design and analysis . For structured development techniques this meant that throughout software development, the developer could conceptualize the system in terms of functions and processes, inputs and outputs. For object-oriented development, on the other hand, the developer thinks throughout in terms of objects, classes, methods, inheritance and the like.

Information systems of the future, such as enterprise resource planning (ERP), groupware, knowledge management and e-business systems, should be designed to match their operational environment. For instance, ERP systems have to implement a process view of the enterprise to meet business goals, 2 tightly integrating all relevant functions of their operational environment. To reduce as much as possible this impedance mismatch between the system and its environment, we outline in this paper a development framework, named Tropos , which is requirements-driven in the sense that it is based on concepts used during early requirements analysis. To this end, we adopt the concepts offered by i* , a modeling framework proposing concepts such as actor (actors can be agents, positions or roles), as well as social dependencies among actors, including goal, softgoal, task and resource dependencies. These concepts are used for an e-commerce example 3 to model not just early requirements, but also late requirements, as well as architectural and detailed design.

2.The first goal is Availability because we propose to allow system agents to automatically decide at run-time which catalogue browser, shopping cart and order processor architecture fit best customer needs or navigator/platform specifications. Moreover, we would like to include different search engines, reflecting different search techniques, and let the system dynamically choose the most appropriate. The second key softgoal in the late requirements specification is Security. To fulfil it, we propose to support in the system’s architecture a number of security strategies and let the system decide at run-time which one is the most appropriate, taking into account environment configurations, web browser specifications and network protocols used. The third goal is Adaptability, meaning that catalogue content, database schema, and architectural model can be dynamically extended or modified to integrate new and future web-related technologies.

Availability is decomposed into Usability, Integrity and Response Time. Network communication may not be very reliable causing sporadic loss of the server. There should be data integrity concerns with the capability of the ebusiness system to do what needs to be done, as quickly and efficiently as possible: in particular with the ability of the system to respond in time to client requests for its services. It is also important to provide the customer with a usable application, i.e., comprehensible at first glimpse, intuitive and ergonomic. Equally strategic to usability concerns is the portability of the application across browser implementations and the quality of the interface. Security has been decomposed into Authorization, Confidentiality and External Consistency. Clients, exposed to the internet are, like servers, at risk in web applications. It is possible for web browsers and application servers to download or upload content and programs that could open up the client system to crackers and automated agents. JavaScript, Java applets, ActiveX controls, and plug-ins all represent a certain degree of risk to the system and the information it manages. Equally important, are the procedures checking the consistency of data transactions.

3.Resource, task and softgoal dependencies correspond naturally to functional 10 and non-functional requirements. Leaving (some) goal dependencies between system actors and other actors is a novelty. Traditionally, functional goals are “operationalized” during late requirements [13], while quality softgoals are either operationalized or “metricized” [14]. For example, Billing Processor may be operationalized during late requirements analysis into particular business processes for processing bills and orders. Likewise, a security softgoal might be operationalized by defining interfaces which minimize input/output between the system and its environment, or by limiting access to sensitive information. Alternatively, the security requirement may be metricized into something like “No more than X unauthorized operations in the system-to-be per year”. Leaving goal dependencies with system actors as dependees makes sense whenever there is a foreseeable need for flexibility in the performance of a task on the part of the system. For example, consider a communication goal “communicate X to Y”. According to conventional development techniques, such a goal needs to be operationalized before the end of late requirements analysis, perhaps into some sort of a user interface through which user Y will receive message X from the system. The problem with this approach is that the steps through which this goal is to be fulfilled (along with a host of background assumptions) are frozen into the requirements of the system-to-be. This early translation of goals into concrete plans for their fulfillment makes systems fragile and less reusable.

4.In Tropos, the information system is represented as one or more actors which participate in a strategic dependency model, along with other actors from the system’s operational environment. In other words, the system comes into the picture as one or more actors who contribute to the fulfillment of stakeholder goals.

• Early requirements, concerned with the understanding of a problem by studying an organizational setting; the output of this phase is an organizational model which includes relevant actors, their respective goals and their inter-dependencies.

• Late requirements, where the system-to-be is described within its operational environment, along with relevant functions and qualities.

• Architectural design, where the system’s global architecture is defined in terms of subsystems, interconnected through data, control and other dependencies.

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