Most developers are well-aware of the concepts of
object-oriented development, but those same concepts originate from a broader approach to the entire software development life cycle known as
object-oriented analysis and design (
OOAD is a technical method of analyzing and designing an application based on that system's
object models (the logical components of the system that interact with one another).
We'll take the time in this article to explore exactly what
object-oriented analysis and
object-oriented designare, how these techniques are typically used in modern development, and any potential advantages or disadvantages you may consider when implementing
OOAD into your own work. Let's get going!
Origins of Object-Oriented Analysis and Design
During the software development life cycle, development is typically broken up into
stages, which are loose, abstract concepts used to separate the activities taking place within each phase of development. Often, these stages might include
maintenance, and so forth.
In the case of stringent development methodologies, such as the waterfall method, these stages are sequential and intended to be completely separate from one another. Thus, when creating an application using the waterfall method, it's unlikely that discoveries made during the
deployment phases can impact the decisions already made during the
design phases. These limitations, along with the strict step-by-step staging process of waterfall-esque models, led to the rise of
iterative models like
object-oriented analysis and design.
OOAD practices have been around for a number of decades, the core ideas and techniques were largely cemented in the collective mind of the development community in the 1990s. An assortment of practitioners and authorities in the industry, working together and on solo endeavors, began to publish a number of books, articles, and techniques that all relied heavily on
OOAD concepts. Some of these publications and methodologies are still well-known and in use today, including the
Unified Modeling Language and the
Rational Unified Process.
What is Object-Oriented Analysis?
object-oriented analysis we must first define what we mean by an
object. The definition of an
object, according to most dictionaries, is "a tangible, material thing." Drilling down a bit more to the realm of computer science, an
object can be most anything in a programmatic sense, from a variable or data model to a function, class, or method. Moving even deeper into the realm of
object-oriented programming, an
object is an instance of a thing that typically represents a real world object and has all the same types of characteristics (
properties), behaviors (
methods), and states (
data). When discussing
OOAD concepts, an
object most closely resembles the
object-oriented programming version of an
object, in that it is a representation of a real world object with behaviors, characteristics, and states.
With that out of the way, we can define
object-oriented analysis (
OOA). In short,
OOA is an iterative stage of analysis, which takes place during the software development life cycle, that aims to model the functional requirements of the software while remaining completely independent of any potential implementation requirements. To accomplish this task via
OOAD practices, an
object-oriented analysis will focus everything through the lens of
objects. This forces
OOA to combine all
states together into one analysis process, rather than splitting them up into separate stages, as many other methodologies would do.
To accomplish this goal, a typical
OOA phase consists of five stages:
- Find and define the objects.
- Organize the objects.
- Describe how the objects interact with one another.
- Define the external behavior of the objects.
- Define the internal behavior of the objects.
For example, a typical implementation of
OOA is to create an
object model for an application. The
object modelmight describe the
characteristics of each object in the system. With this information established for each object, the design process that follows is much simpler.
What is Object-Oriented Design?
The process of
object-oriented design is really just an extension of the
object-oriented analysis process that preceded it, except with a critical caveat: the consideration and implementation of
constraints. For example, with an
analyzed object in hand, such as an
object model, we must now consider how that object would actually be designed and implemented, which will often require the application of constraints, such as software or hardware platforms, time and budgetary limitations, performance requirements, developer aptitude, and so forth.
Put another way, the
OOD process takes the theoretical concepts and ideas planned out during the
OOA stage, and tries to find a way to design and tangibly implement them, usually via code using whatever language and platforms the development team has settled upon. If
OOA is the what, then
OOD is the how.
Advantages of Object-Oriented Analysis and Design
- Encourages Encapsulation: Since everything within
OOADrevolves around the concept of
object-orientedvariety), one of the biggest advantages of
OOADis that it encourages planning and development of systems that are truly independent of one another. Just like a
object-orientedtechniques, all the systems and objects produced during an
OOADdevelopment life cycle can be mixed and matched as necessary, since they will ideally be built as completely self-contained entities.
- Easy to Understand: Since
OOADprinciples are fundamentally based on real world objects, it's quite easy for everyone on the team to quickly understand what an object name means or how a particular behavior, well, behaves. This makes the overall development life cycle a much smoother process, particularly if your team needs to frequently interact with customers or other non-technical users about the objects and components in the system. In such cases, most people still understand how system components and modelled objects work when they're based on real world objects and ideas.
Disadvantages of Object-Oriented Analysis and Design
- Ill-Suited to Procedural Applications: Given the object-oriented nature of
OOAD, it is quite difficult (although not impossible) to practice
OOADtechniques within a procedural programming language, or often to apply the techniques to non-object business logic. Whereas procedural applications are often logically bound by concepts of scope and modularity, object-oriented applications, of course, emphasize objects that simulate the real world, making
OOADmethods ill-suited for procedural languages and applications.
- Too Complex for Simple Applications: While arguably not a disadvantage that is applicable to all projects, it's certainly the case that
OOADpractices are generally not ideal for simpler projects. Many developers have their own personal hard and fast rules to help when deciding whether a project should be procedural or object-oriented, but in most cases, the more basic the needs of the application, the more likely a less-structured, procedural approach is the best fit. As always, we must always use our own best judgment.