Responsibility-driven design

Responsibility-driven design focuses on the objects as behavioral abstractions which are characterized by their responsibilities. The CRC-card modelling technique is used to generate these behavioral abstractions. The rest of the object structure including data attributes are assigned later, as and when required. This makes the design follow type hierarchy for inheritance which improves encapsulation and makes it easier to identify abstract classes. It can also group the classes together based on their clients which is considered a unique ability. A good object-oriented design involves an early focus on behaviors to realize the capabilities meeting the stated requirements and a late binding of implementation details to the requirements. This approach especially helps to decentralize control and distribute system behavior which can help manage the complexities of high-functionality large or distributed systems. Similarly, it can help to design and maintain explanation facilities for cognitive models, intelligent agents, and other knowledge-based systems. ==Building blocks==

In their book Object Design: Roles, Responsibilities and Collaborations, the authors describe the following building blocks that make up responsibility-driven design. • Application: A software application is referred to as a set of interacting objects. • Collaborations: A collaboration is defined as an interaction of objects or roles (or both). These cards are split up into an unlined and a lined side. • Content of lined side: On this side the candidate's name, its responsibilities and its collaborators are recorded. • Hot Spot Cards: Hot Spot Cards are used for recording variations with just enough detail so you can discriminate important difference. Similar to CRC cards, these are also created from index cards. It is a logical grouping of collaborators. These are further categorized according to their usage scenario. • Public Responsibilities: Public responsibilities are the responsibilities an object offers as services to others and the information it provides to others. • Private Responsibilities: Private responsibilities are the actions an object takes in support of public responsibilities. They are further categorized based on what they do. • Subordinate Responsibilities: These include the major steps in each subresponsibility. Role Stereotypes: Role stereotypes are simplified roles that come with predefined responsibilities. There are several categories. • Controller: Object implementing this role makes decisions and closely directs the action of other objects. • Interfacer: This role transforms information and requests between distinct parts of an application. • Service Provider: This role performs work and offers computing services. • Structurer: This role maintains relationships between objects and information about those relationships. ==Control style==

An important part in the responsibility-driven design process is the distribution of control responsibilities that results in developing a control style. A control style is concerned about the control flow between subsystems. • Concept of Control : The responsibilities and collaborations among the classes. • Control Centers : An important aspect of developing a control style is the invention of so-called control centers. These are places where objects charged with controlling and coordinating reside. • Control Style Variations : A control style comes in three distinct variations. These are not precise definitions though since a control style can be said to be more centralized or delegated than another. Centralized control style This control style inflicts a procedural paradigm on the structure of the application and places major-decision making responsibilities in only a few objects or a single object. ;Types • Call-return model : The control of the objects in the application is in hierarchical way. Control starts at root and moves downwards. It is used in a sequential model. • Manager model : The control of the objects in the application is in with only one object. Generally, it is implemented in concurrent models. It can also be implemented in sequential model using case statement. ;Advantages • Application logic is in one place. ;Disadvantages • Control logic can get overly complex • Controllers can become dependent on information holders' contents • Objects can become coupled indirectly through the actions of their controller • The only interesting work is done in the controller ;When to use When decisions to be made are few, simple, and related to a single task. Delegated control style A delegated control style lies in between a centralized and dispersed control style. It passes some of the decision making and much of the action to objects surrounding a control center. Each neighboring object has a significant role to play. It can also be called as event driven model, where the control is delegated to the object requesting it to process the event. ;Types[reference] • Broadcast model : An event is broadcast to all objects in the application. The object which can handle the event can acquire the control. • Interrupt-driven model : There will be the interrupt handler to process the interrupt and passes to some object to process it. ;Advantages • It is easy to understand. • Though there is an external coordinator, Objects can be made smarter to know what they are supposed to do and can be reused in other applications. • Delegating coordinators tend to know about fewer objects than dominating controllers. • Dialogs are higher-level. • It is easy to change as changes typically affect fewer objects. • It is easier to divide design work among team members. ;Disadvantages • Too much distribution of responsibility can lead to weak objects and weak collaborations ;When to use When one wants to delegate work to objects that are more specialized. Clustered control style This control style is a variation of the centralized control style wherein control is factored among a group of objects whose actions are coordinated. The main difference between a clustered and delegated control style is that in a clustered control style, the decision making objects are located within a control center whereas in a delegated control style they are mostly outside. Dispersed control style A dispersed control style does not contain any control centers. The logic is spread across the entire population of objects, keeping each object small and building in as few dependencies among them as possible. ;Advantages • None ;Disadvantages • When you want to find out how something works, you must trace the sequence of requests for services across many objects • Not very reusable because no single object contributes much ;When to use Never. Preferred control style After extensive results of experiments conducted, only the senior management has the necessary skills to make use of delegated control style and centralized control style benefits programmers. There is no context mentioned about the mid-level employees. ==References==