Some of these slides were excerpted from:

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Team-Based DevelopmentISYS 321

• Some of these slides were excerpted from
• Object-Oriented Systems Analysis and Design
• Joey F. George, Dinesh Batra, Joseph S. Valacich,
  Jeffrey A. Hoffer
• Chapter 12 Design Elements

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What Is a Design Element?

• Either a design class or a component
• Design Class an enhanced version of an analysis
  class that includes details regarding attributes
  and methods, including visibility, arguments, and
  data types.
• Component a replaceable part of a system that
  provides a clearly defined function through a set
  of interfaces.

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What Is a Design Architecture?

• An overall blueprint of the design of a system.
• Goal of design architecture ability to scale
  and evolve over time.
• Enterprise Application Design (EAD) the process
  of designing applications that embrace change
  (integration is not a problem)

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What Is a Tiered (or Layered) Architecture?

• The partitioning of a system into layers such
  that each layer performs a specific type of
  functionality and communicates with the layers
  that adjoin it.
• Options
• Single-tier
• Two-tier
• Three-tier
• N-tier

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Single-Tier Architectures

• One computer performing all tasks
• Either a standalone PC, or a mainframe servicing
  many dumb terminals
• Rare for new systems, not very scalable

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Two-Tier Architectures

• Client-Server architecture
• Client Application layer (front-end), performs
  business rules and user interface
• Server Database layer (back end), provides data
  access
• Middleware the communication interface between
  client and server

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What Is Middleware?

• Software that provides one set of interfaces for
  connection to a client and another set of
  interfaces for connection to a server, thereby
  providing the possibility of connections between
  one of several clients with one of several
  servers.
• For instance, a system in which the front-end GUI
  (application layer) communicates with a database
  using ODBC (Open Database Connectivity
  middleware).

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Limitations of Client-Server Architectures

• Thick clients heavy burden placed on each
  client machine (too much processing)
• Application changes need to be distributed to
  many clients
• Typically use proprietary technologies, hindering
  application integration

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Three-Tier Architectures

• Three layers are
• Presentation front tier, providing user
  interface, perhaps with formatting and
  constraint-checking rules
• Business rules middle tier, addressing logic
  and decisions for the system, sometimes called
  application layer
• Data back tier, addressing data storage and
  access, with some rules regarding data integrity

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Note presentation, business logic, and or data
can be spread across multiple layers, creating
N-tier architectures.
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Mapping from Analysis to Design Classes

• 1 Analysis Class ? 1 Design Class
• 1 Analysis Class ? n Design Classes(i.e.you may
  find you have 2 categories of Employee, FT and PT
  employee)
• n Analysis Classes ? 1 Design Class(i.e. you
  may want to combine classes such as in the case
  of denormalization)
• n Analysis Classes ? 1 Package(i.e. you may want
  to combine a group of classes with similar
  functionality, such as Customer and Products
  Purchased under CustomerRelations)
• n Analysis Classes ? 1 Component(i.e. you may
  need to purchase a commerically available
  component rather than build in-house)

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Characteristics of Components

• Used for specific commonly used purpose
• Collection of classes and interfaces
• Hidden implementation details
• Plug-and-play capability
• Third-party developed, typically in binary form
• Reusable in many applications
• Well-tested and relatively error-free

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What Is a Component Standard?

• An agreed-upon format for defining interfaces and
  implementations of components
• Examples
• Microsoft COM
• OMGs CORBA
• Sun Microsystems Enterprise Java Beans (EJB)
• Database Middleware Standards (ODBC, ADO, JDBC)
• XML/SOAP

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COM

• Component Object Model (COM) from Microsoft
• Run-time environment for middle-tier components
• Supports transactions, identity, and security
  services, and allows components to call each
  other locally or remotely through a messaging
  service

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CORBA

• Common Object Request Broker Architecture
• Published by Object Management Group (OMG)
• Component standard for distributed and
  heterogeneous network
• Objects written in different languages
  communicate through Interface Definition Language
• Interface is managed by Object Request Brokers
  (ORBs)

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EJB

• Enterprise Java Beans
• Component-based distributed computing
  architecture
• EJB is a server-side component model for managing
  objects in a distributed environment
• EJB requires CORBA for communications

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Database Middleware Standards

• Microsofts ODBC Open Database Connectivity
• Microsofts ADO ActiveX Data Objects
• Suns JDBC Java Database Connectivity

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Comparison of OMG, Microsoft, and Sun

• Limitations
• Tightly coupled
• Binary
• Proprietary

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XML and SOAP

• Text-based, loosely coupled, non-proprietary
  internet-oriented standard for inter-layer
  communication
• eXtensible Markup Language (XML) method for
  putting structured data into text format, similar
  to HTML
• Simple Object Access Protocol (SOAP) XML-based
  protocol for exchanging messages between
  applications operating in different layers

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What Is a Framework?

• A collection of components, consisting of code
  and interfaces written in a specific language,
  that solves or helps build applications.
• Two main competitors
• Microsoft .NET
• Sun Java 2 Enterprise Editiion (J2EE)

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Microsoft .NET

• Development framework that integrates COM and
  Active Server Pages (ASP) technologies for B2C
  applications, with support for XML/SOAP Web
  services for B2B applications
• ActiveX OLE/COM based component
• ADO, ADO .NET database middleware
• ASP, ASP.NET dynamic HTML generation

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Sun J2EE

• Java 2 Enterprise Edition
• Development framework that provides a
  specification of architectural components
  designed to work together to define a complete
  enterprise architecture, with support for
  XML/SOAP and Web services
• EJB Java-based component standard
• JDBC database middleware
• Java Server Pages, Servlets dynamic HTML
  generation

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In UML, packages are represented as rectangles
with tabs in the top left corner.
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What Is a Design Class Diagram?

• A design class diagram shows the data types of
  the attributes, the return types and arguments of
  the operations, and the visibility specifications
  for all attributes and operations.
• Signature the return type, name, and argument
  list of a method
• Interfaces to classes are based on signatures.

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Guidelines for Allocating Responsibilities

• Information access done by information expert
• Object creation done by aggregating class
• Aim for loose coupling
• Aim for high cohesion

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Recap

• After studying this chapter we learned to
• Understand the different design architecture
  configurations.
• Understand the use of components in systems
  design.
• Understand the different component standards.
• Map an analysis class diagram into a design class
  diagram.

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• Any Questions?