Unit 7 Patterns and Frameworks

Key Concepts Design classes Components Design architectures EAD Patterns Packages Frameworks

What Is a Design Element? 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.

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.

Patterns Overview A pattern is an abstraction. A pattern represents a proven way to solve a problem. A pattern applies to multiple pieces of software, not one specific solution. A pattern allows you to leverage existing designs A pattern provides a way for designers to communicate.

What is a Pattern? Context: a situation in which the problem occurs. Problem: the recurring problem. Solution: a proven way to resolve the problem.

Types of Patterns Architecture pattern Describes the architecture of a system Design pattern More narrow in scope Applies to a subsystem Not language-specific Idiom Narrow in scope Applies to only a specific programming language

12-8 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

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 Also called "monolithic"

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

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.

Limitations of Client-Server Architectures Thick clients – heavy burden placed on each client machine Application changes need to be distributed to many clients Typically use proprietary technologies, hindering application integration

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

Note: presentation, business logic, and or data can be spread across multiple layers, creating N-tier architectures.

Presentation, business logic, and or data can be spread across multiple layers, creating N-tier architectures.

Mapping from Analysis to Design Classes 1 Analysis Class  1 Design Class 1 Analysis Class  n Design Classes n Analysis Classes  1 Design Class n Analysis Classes  1 Package n Analysis Classes  1 Component

What is a Software Component? A software element with a well-defined interface and functionality for a specific purpose that can be deployed in a variety of applications using plug-and-play capability Usually purchased from a third party

Characteristics of Components Used for specific commonly used purpose Collection of classes and interfaces Hidden implementation details Plug-and-play capability Usually distributed in binary, executable form Third-party developed Reusable in many applications Well-tested and relatively error-free Written in any language that supports component standard’s interface conventions

Component Terminology Run-time Environment – classes and components required to support services like handling secure transactions during run-time Transaction – all-or-nothing unit of business work. Requires ACID: Atomicity Consistency Isolation Durability

What Is a Component Standard? An agreed-upon format for defining interfaces and implementations of components Examples: Microsoft COM/COM+/DCOM OMG’s CORBA Sun Microsystem’s Enterprise Java Beans (EJB) Database Middleware Standards (ODBC, ADO, JDBC) XML/SOAP

COM/COM+/Distributed COM (DCOM) 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

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 (IDL) Interface is managed by Object Request Brokers (ORBs)

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

Database Middleware Standards Microsoft’s ODBC – Open Database Connectivity Microsoft's OleDb Microsoft’s ADO – ActiveX Data Objects Sun’s JDBC – Java Database Connectivity

Comparison of OMG, Microsoft, and Sun Limitations: 1.Tightly coupled 2.Binary 3.Proprietary

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

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 Edition (J2EE)

12-29 Microsoft.NET Development framework for B2C applications, with support for XML/SOAP Web services for B2B applications Large library of extensible objects Interoperability with ActiveX – OLE/COM based component ADO, ADO.NET – database middleware ASP, ASP.NET – dynamic HTML generation Enterprise Services – Library for developing Enterprise applications

Features of Microsoft.NET Framework Visual Studio.NET – development environment C#, Visual C++, and Visual Basic.NET – the three main programming languages for developing.NET applications Common Language Runtime (CLR) – the runtime environment that loads/executes code, manages memory, provides security, exception handling and interoperability

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

Features of Java J2EE Java Virtual Machine (JVM) – interpreter for executing Java compiled code (bytecode) Remote Method Invocation (RMI) – middleware that allows Java programs running on different computers to access each others’ objects/methods Applet – Java program that runs in the browser as part of a web page Servlet – Java program executed on a Web server Java Server Pages (JSP) – technology that mixed Java and HTML for dynamic web page generation

What is a Package? A general-purpose mechanism for organizing design elements into groups Package diagram – a diagram that shows the packages and the relationships between them

Characteristics of Packages Cohesiveness Allocation of resources among development teams User types Propensity to change Development phase Separate utilities from system-specific components

In UML, packages are represented as rectangles with tabs in the top left corner. Dependencies between packages are shown with dashed arrow lines.

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.

Verifying Responsibility Allocation Pattern – a named description of a problem and solution that can be applied to new contexts Responsibility assignment in patterns: Information expertise (expert pattern) Object creation (creator pattern) Loose coupling and strong cohesion

Visibility The characteristics of an attribute or an operation that reveal whether it can be accessed directly Three levels of visibility: Public – visible to any requesting object Private – visible to the owning object only Protected – visible to the owning object, objects of the same class, and objects of subclasses

Attribute Types In Design class diagram, attribute types are explicitly displayed In the following slide, you see: Visibility of attributes and operations Attribute types Responsibilities represented by methods Full method signatures including return types and parameters

Visibility is shown by minus signs (private) or plus signs (public) Attribute types and full signatures are shown