Object-oriented Modeling And Design With Uml Pdf

[Lorriane Nasuti]

Intentionof object oriented modeling and design is to learn how to apply object -oriented concepts to all the stages of the software development life cycle.Object-oriented modeling and design is a way of thinking about problems using models organized around real world concepts. The fundamental construct is the object, which combines both data structure and behavior.

The class diagram is used to show the class model.The class diagram shows the class name followed by the attributes followed by the functions or the methods that are associated with the object of the class.Goal in constructing class model is to capture those concepts from the real world that are important to an application.

This is one of those anti-patterns that's been around for quite along time, yet seems to be having a particular spurt at the moment. Iwas chatting with Eric Evans on this, and we've both noticed they seemto be getting more popular. As great boosters of a proper DomainModel, this is not a good thing.

The basic symptom of an Anemic Domain Model is that at firstblush it looks like the real thing. There are objects, many namedafter the nouns in the domain space, and these objects are connectedwith the rich relationships and structure that true domain modelshave. The catch comes when you look at the behavior, and you realizethat there is hardly any behavior on these objects, making themlittle more than bags of getters and setters. Indeed oftenthese models come with design rules that say that you are not to putany domain logic in the the domain objects. Instead there are a set ofservice objects which capture all the domain logic, carrying out all the computation andupdating the model objects with the results. These serviceslive on top of the domain model and use the domain model for data.

The fundamental horror of this anti-pattern is that it's socontrary to the basic idea of object-oriented design; which is tocombine data and process together. The anemic domain model is reallyjust a procedural style design, exactly the kind of thing that objectbigots like me (and Eric) have been fighting since our early days inSmalltalk. What's worse, many people think that anemic objects arereal objects, and thus completely miss the point of whatobject-oriented design is all about.

Now object-oriented purism is all very well, but I realize that Ineed more fundamental arguments against this anemia. In essence theproblem with anemic domain models is that they incur all of the costsof a domain model, without yielding any of the benefits. The primarycost is the awkwardness of mapping to a database, which typicallyresults in a whole layer of O/R mapping. This is worthwhile iff youuse the powerful OO techniques to organize complex logic. By pullingall the behavior out into services, however, you essentially end upwith TransactionScripts, and thus lose the advantages that the domain model canbring. As I discussed in P of EAA, DomainModels aren't always the best tool.

It's also worth emphasizing that putting behavior into the domainobjects should not contradict the solid approach of using layering toseparate domain logic from such things as persistence and presentationresponsibilities. The logic that should be in a domain object isdomain logic - validations, calculations, business rules - whateveryou like to call it. (There are cases when you make an argument forputting data source or presentation logic in a domain object, butthat's orthogonal to my view of anemia.)

One source of confusion in all this is that many OO experts dorecommend putting a layer of procedural services on top of a domainmodel, to form a Service Layer. But this isn'tan argument to make the domain model void of behavior, indeed servicelayer advocates use a service layer in conjunction with a behaviorallyrich domain model.

Application Layer [his name for Service Layer]: Defines the jobs the software is supposed to doand directs the expressive domain objects to work out problems. Thetasks this layer is responsible for are meaningful to the business ornecessary for interaction with the application layers of othersystems. This layer is kept thin. It does not contain business rulesor knowledge, but only coordinates tasks and delegates work tocollaborations of domain objects in the next layer down. It does nothave state reflecting the business situation, but it can have statethat reflects the progress of a task for the user or the program.

Domain Layer (or Model Layer): Responsible for representingconcepts of the business, information about the business situation,and business rules. State that reflects the business situation iscontrolled and used here, even though the technical details of storingit are delegated to the infrastructure. This layer is the heart ofbusiness software.

I don't know why this anti-pattern is so common. I suspect it'sdue to many people who haven't really worked with a proper domainmodel, particularly if they come from a data background. Sometechnologies encourage it; such as J2EE's Entity Beans which is one ofthe reasons I prefer POJO domain models.

In general, the more behavior you find in the services, the more likely you are to be robbing yourself of the benefits of a domain model. If all your logic is in services, you've robbed yourself blind.

Moreover, the OO system is more than just the syntax. The encapsulation makes the code more organized. Although julia has module, associating a function with a particular structure could be useful in some circumstances.

Having said that, I found this post on Reddit, where Eigenspace described a way to achieve what I described above in julia. Hopefully this can be useful for people who also want some lightweight OO support in julia.

Yes, different programming languages have different styles. Nonetheless, different styles do not necessarily exclude each other. For example, OOP is part of the design of Python and very popular in the community, but there is an official library for functional programming, which allows people to write code in a different style when it is more suitable.

Personally speaking, I believe the function-oriented style is more natural for scientific computing in most situations, and this is one reason why I like julia. However, there are situations where other styles are more natural. For example, for agent-based modeling I think OOP is more natural.

The full OOP has much more than the foo.func() syntax, for example, inheritance. Some people said julia has already supported OOP and multiple dispatch is more general than OOP. This claim oversimplifies OOP, which is a quite complicated beast, more than just a function call syntax or polymorphism. Therefore, writing foo.func() is far away from OOP. (This is actually called UFCS, and has nothing to do with OOP.)

I reckon it would be relatively* easy to create a macro to transform obj.foo(...) into foo(obj,...) (and maybe something similar on the method definition side) and thus emphasize an object oriented thinking.

But to summarize briefly, any inheritance structure can be restructured in terms of composition, and in many cases should be, even in OOP languages. Inheritance often seems like a natural and intuitive way of structuring code but almost always creates problems in the long-run; in my experience, the most common anti-patterns are fragile base classes, subclass repetition, and god-types, all of which are typically rampant in inheritance-heavy code. Composition has its own pitfalls but is generally a much more scalable pattern and is also better for encapsulation.

My point is the syntax. Of course we can turn everything into the func(obj, ...) way, but in the situation where the action is tightly related to the object, it is possible that the other way makes more sense. These situations are indeed relatively rare in science and math, but they do exist and I could not see why writing code in this style is harmful in those circumstances.

Object-oriented analysis and design (OOAD) is a technical approach for analyzing and designing an application, system, or business by applying object-oriented programming, as well as using visual modeling throughout the software development process to guide stakeholder communication and product quality.

OOAD in modern software engineering is typically conducted in an iterative and incremental way. The outputs of OOAD activities are analysis models (for OOA) and design models (for OOD) respectively. The intention is for these to be continuously refined and evolved, driven by key factors like risks and business value.

In the early days of object-oriented technology before the mid-1990s, there were many different competing methodologies for software development and object-oriented modeling, often tied to specific Computer Aided Software Engineering (CASE) tool vendors. No standard notations, consistent terms and process guides were the major concerns at the time, which degraded communication efficiency and lengthened learning curves.

Some of the well-known early object-oriented methodologies were from and inspired by gurus such as Grady Booch, James Rumbaugh, Ivar Jacobson (the Three Amigos), Robert Martin, Peter Coad, Sally Shlaer, Stephen Mellor, and Rebecca Wirfs-Brock.

In 1994, the Three Amigos of Rational Software started working together to develop the Unified Modeling Language (UML). Later, together with Philippe Kruchten and Walker Royce (eldest son of Winston Royce), they have led a successful mission to merge their own methodologies, OMT, OOSE and Booch method, with various insights and experiences from other industry leaders into the Rational Unified Process (RUP), a comprehensive iterative and incremental process guide and framework for learning industry best practices of software development and project management.[1] Since then, the Unified Process family has become probably the most popular methodology and reference model for object-oriented analysis and design.

An object contains encapsulated data and procedures grouped to represent an entity. The 'object interface' defines how the object can be interacted with. An object-oriented program is described by the interaction of these objects. Object-oriented design is the discipline of defining the objects and their interactions to solve a problem that was identified and documented during object-oriented analysis.

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