The Mysteries of Business Object - Part 1
by Samudra Gupta
Business Objects are present in any real-life application. In the
world of application architecture, Business Objects are a constant
challenge to the designers to achieve the right level of granularity
and reusability. The myths surrounding the Business Objects often
blur the focus and bloat the system design. In this series, we will
attempt to clear the cloud surrounding the Business Objects. In the
first part, we cover the ground work of defining Business Objects,
and compare different strategies for implementing them. Also, we
shall discuss embedding business logic and data validation with
Business Objects and see how to expose Business Objects to the client
application.
What are Business Objects?
There are many views of what the definition of a Business Object is. However, the
most commonly accepted definitions of a Business Object can be stated as
follows:
Business Objects represent tangible entities within an
application that the users create,access and manipulates while
performing a Use Case. The Business Objects within a system are
typically stateful, persistent and long-lived. Business Objects
contain business data and models the business behavior.
From the above definition of Business Object, we might be able
to gather a vague idea of how to identify and define Business
Objects in our system, but still there are many questions that
will arise during the design phase of the application. For
example, consider the following questions:
- Should the Business Objects need to be always user-
facing? Can we have a Business Object that the user never
interacts with?
- Why Business Objects need to be stateful? Can I define a
Business Object that does not maintain state?
- How and where do we persist the Business Object?
- What about validation of the data within a Business Object?
- How do we handle the concurrency and transaction issues with
a Business Object?
And there are many more.... we will try
to address these issues and few more in the following sections of
this article.
The Nature of Business Objects
The Business Objects are the core of any application. A system
will generally have more than one Business Objects interacting
with each other to offer a whole range of functionalities. Once
the business process is complete the Business Objects tend to
persist themselves in a permanent data-store for future use.
Typically, when modelling an application, business objects come
out of the nouns defined within a use case statement. These
Business Objects are acted upon by the external actors such as
User of the System. In this sense, the Business Object is
client-facing. On the other hand, there are some Business
Objects, which are acted upon by the system itself. For example,
in an order-processing system, there may be a Business Object,
which validates all the orders gathered on a particular day and
analyses all the orders over $1000 and processes them in a
priority basis. This Business Object will never be exposed to
the client domain but will be used by the System itself.
We have discussed before that Business Objects encapsulate
business data and the behavior. For example, a Customer Business
Object can hold data about the details of a particular customer
and can also expose the behavior to change the customer contact
details.
Now one important thing to note is that Business Objects are not
same as data objects. The distinction between Business Objects
and Data Objects is that the Data Objects purely hold data and
has no behavior. A Business Object might be composed of one or
more Data Objects. For example, Customer Business Object might
be composed of a data object called CustomerData.
Typically, Business Objects persist themselves into a permanent
data-store such as database. However, Business Objects may or
may not preserve their state between two consecutive calls to
the same Business Object. Depending upon whether the Business
Object should maintain state between two calls or not, the
Business Object becomes stateful or stateless. This concept is
familiar to the EJB developers who often create a stateful
session bean. Typically, when a business process takes more than
one call to the Business Object to complete the process, we may
need to maintain the state between those calls. Otherwise, if it
is always a one call to do a business process to a Business
Object, the Business Object does not need to maintain its state
and can be implemented as stateless.
Thus, as far as Business Objects are concerned they can be
implemented either stateful or stateless. In some cases, however
it is more appropriate to design the Business Objects to be
stateful. For example, in a Customer Order Processing
Application, assume that the user can add more than one item to
the shopping cart and finally press the checkout button to
complete the process. You will need to have the Business Object
to capture each order item in a shopping cart and it needs to be
stateful in order to hold the complete order list. The Business
Object might finally persist the order information to a
database, when the user has checked out.
Often, people get confused over maintaining state and persisting
state. Maintaining state means preserving the object state
within the same business process and persisting state will mean
that storing the final state of the object in a permanent store
for future reference. A stateful Business Object will lose its
state, if the component responsible for the state management
shuts down (e.g. The application server shuts down) but the
persistent storage operates independent of the application
container.
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