Booch's object identification approach requires a processing narrative of the given problem to be first developed. The processing narrative describes the problem and discusses how it can be solved. The objects are identified by noting down the nouns in the processing narrative. Synonym of a noun must be eliminated. If an object is required to implement a solution, then it is said to be part of the solution space. Otherwise, if an object is necessary only to describe the problem, then it is said to be a part of the problem space. However, several of the nouns may not be objects. An imperative procedure name, i.e., noun form of a verb actually represents an action and should not be considered as an object. A potential object found after lexical analysis is usually considered legitimate, only if it satisfies the following criteria:
Retained information. Some information about the object should be remembered for the system to function. If an object does not contain any private data, it can not be expected to play any important role in the system.
Multiple attributes. Usually objects have multiple attributes and support multiple methods. It is very rare to find useful objects which store only a single data element or support only a single method, because an object having only a single data element or method is usually implemented as a part of another object.
Common operations. A set of operations can be defined for potential objects. If these operations apply to all occurrences of the object, then a class can be defined. An attribute or operation defined for a class must apply to each instance of the class. If some of the attributes or operations apply only to some specific instances of the class, then one or more subclasses can be needed for these special objects.
Normally, the actors themselves and the interactions among themselves should be excluded from the entity identification exercise. However, some times there is a need to maintain information about an actor within the system. This is not the same as modeling the actor. These classes are sometimes called surrogates. For example, in the Library Information System (LIS) we would need to store information about each library member. This is independent of the fact that the library member also plays the role of an actor of the system.
Although the grammatical approach is simple and intuitively appealing, yet through a naive use of the approach, it is very difficult to achieve high quality results. In particular, it is very difficult to come up with useful abstractions simply by doing grammatical analysis of the problem description. Useful abstractions usually result from clever factoring of the problem description into independent and intuitively correct elements.
