Information system architectures and architecting

1. Information system architectures and architecting A practical tour Einar Landre Cell Network AS einar.landre@cellnetwork.no

2. Topics covered • Introduction • Definitions and terminology • History of information systems and their software architectures • Client / Server • Web • Components • Services • Future trends and requirements • From domain model to code – A practical tour • Levels of design • System decomposition • Services • Academic foundation • Design by contract, Open-Closed, Liskov, Dependency inversion, Package stability • References

3. Introduction

4. Ancient architecture Facts Cheops (Khufu) height = 280 cubits perimeter = 1760 cubits perimeter = 2*p*height 1:43.200 scale model of earth Kings chamber 3-4-5 triangle cubit = 52.35 cm

5. Architecting a dog’s house Can be built by one person Requires Minimal modeling Simple process Simple tools

6. Architecting a house Built most efficiently and timely by a team Requires Modeling Well-defined process Power tools

7. Capacity Fail safe Availability Fault tolerance Performance Throughput Technology churn Resilience Forces in software Functionality Cost Compatibility The challenge over the next 20 years will not be speed or cost or performance; it will be a question of complexity. Bill Raduchel, Chief Strategy Officer, Sun Microsystems Our enemy is complexity, and it’s our goal to kill it. Jan Baan

8. Defining architecting and architecture • Architecting, the planning and building of structures, is as old as human societies and as modern as the exploration of the solar system. • Architecting, the art and science of building systems. • Eberhardt Rechtin, The art of systems architecting • Architecture–The set of design decisions about any system (or smaller component) that keeps its implementors and maintainers from exercising needles creativity. • A (software) systems architecture consists of: • The structure of it’s parts (including design-time, test-time, runtime hardware and software parts). • The nature and relevant external visible properties of those parts (modules with interfaces, hardware units, objects). • The relationships and constraints between them.

9. Software architecture • Defines how the software is built • Acts as the knowledge base of the software • Foundation for improvement • Foundation for change • Foundation for new features • Characteristics of a good architecture • Built from recognizable patterns and archetypes • Facilitates change and extension • Supports the open closed design principle • Easy to understand • Supports the driving requirements • Clear separation of concern • Balanced distribution of responsibility • Balances economic and technical constraints

10. Architecting versus Engineering • Architecting, deals largely with unmeasurables using non quantitative tools and guidelines based on practical lessons learned (heuristic) • Software design patterns • Best practices • Engineering, deals almost entirely with measurables using analytical tools derived from mathematics and the hard sciences • Proven reliability of a system • Formal validation and verification of correctness • Response time requirements

11. Architecture depends on purpose • Architectures are tightly connected to their purpose, and to some extent they are only understood through their purpose • The pyramids? • To be successful a architecture must meet two requirements: • Acceptable cost • Acceptable time • Some architectures has been stable for 100 years • Automobiles • Airplanes • Ships • Railroad systems • Others close to thousand • Cathedrals

12. Software as critical system component • Software – the centerpiece of complex system design • Airplanes • Ships – (The frigate project, probably the largest IT project in the country) • Healthcare • Business (banking, retail, public services, traditional industry) • Classicalsystems engineeringis based onDecomposition & Integration • The system hierarchy • Software become a sub-system of its processor unit • Software architectures are layered • Library units call another library unit • Software and hardware hierarcys become disconnected • The engine control software is a subsystem of the engine. • The user interface is a subsystem of the dash board. • The software architecture is layered (user interaction and engine control) • Understanding this is critical when architecting software intensive systems

13. The situation illustrated Car Engineer View Software Engineer View Car User Interface Communication Dashboard Engine Controller Engine Control View Engine Controller Both views are correct, but their purpose and target group differs

14. Purpose System System Architecture Software Architecture System and software architecture dependencies • System - response to a need/problem • Bank self service • Mobile communication system • Naval communication systems • Energy supply system • System architecture (software intensive) The structures and parts of a system • Defines software environment • Naval communication system • Satellites, phones, antennas,…. • Software architecture The structures and parts of software • Includes design time, test times, language constraints and interfaces

15. Summary • Today I am more convinced than ever. Conceptual integrity is central to product quality. Having a system architect is the most important step toward conceptual integrity. • Fredrick P. Brooks, JR • The mythical man month after twenty years

16. History of information systems and their software architectures

17. 3270 Terminal(1) 3270 Terminal(1) 3274 Terminal Controller 3274 Terminal Controller MVS 3270 Terminal(32) 3270 Terminal(32) CICS V T A M D A T A TSO RJE In 1974 IBM released its Systems Network Architecture (SNA) 3705 Front-End Controller Phone Lines 3705 Front-End Controller • Before SNA terminals was physically attached to programs • SNA enabled effective use of thousands of terminals (users) • Application areas involved: • 3270 terminal (synchronous terminal and printer) • Transaction Processing, Time sharing and Batch • The almighty god in a SNA network was VTAM (Virtual Telecommunications Access Method) • Software architectures still monolitic (user interface, data and algorithms in one chunk) • 1974 was also the year Kerf & Kahn released the TCP/IP specification

18. Client / Server – The architecture of the 1980ties Client Server protocol Files & Databases User Interface & Business Logic • Originally used to scale mini computer networks • Client machine(s) responsible for user interaction and business logic • Server machine(s) responsible for data and common services as print • Applied at both at system and software levels • Boosted by the BSD Unix release embedding the TCP/IP protocol stack in 1981 • Unix workstations (SUN) and later PC the dominant users of the architecture • Identified problems: • Tight coupling of client and server made changes hard • Distribution of software to many clients • Lack of scalability in the large • Sensitive to network latency • Unreliable outside local area network environment • Client and Server share state

19. Internet and Web oriented architectures (1994 – today) HTTP Transport Client Server Internet Browser Web Server • Browser installed on any type of computer with graphical user interface attached to Internet • http://www.cellnetwork.no - The Unified Resource Locator (URL) was born • Web server provided textual content formatted in HTML • Java launches and become famous for its ability to download code (the applet) • Web servers evolve to handle dynamic content • Common Gateway Interface (CGI) and Perl • Programs are impossible to maintain • Sun launches the servlet concept, enabling server side dynamic HTML management • The need to simplify user interface programming results in tag libraries • Sun – Java Server Pages (JSP), MS got ASP and Open Source got PHP • New server side technologies has emerged including J2EE and MS .NET

20. Computer Computer Component Component Component Component Component architectures (1990 – today) TCP/IP Network • Convergence of distributed object models (CORBA) and Transaction Processing Monitors • Enterprise Java Beans (EJB) • Distributed Component Object Model (DCOM) from Microsoft • Move software towards assembly of “pluggable-parts” • Based on the concept of hiding implementation from specification • Object Oriented • EJB uses the Java interface construct combined with Remote Method Invocation • Network transparent • Identified problems • Solutions become more rigid than first anticipated (not as easy to plug) • More TP monitor than distributed objects • Sensitive to network latency

21. The N-tier web architecture – practical use of components HTTP Transport Server - side Client Internet Web Server Application Server (EJB) Database Server Browser • The server side is dominated by the N-tier architecture • Web, Application and Database servers are large software components • They can reside on one or more physical computers • The architecture provides scalability and redundancy • Based on the same principles as IBM applied in 1974 • Designed to handle thousands of interactive users • Identified problems: • More rigid than first anticipated • More TP monitor than distributed object model • Sensitive to network latency

22. Beyond components – Network to Network Services Network to Network XML Network Network system system • Systems in different networks can communicate • Also known as web services • Supports synchronous and asynchronous communication • Supported by mechanisms such as • UDDI (Universal Description, Discovery & Integration) • SOAP (Simple Object Access Protocol – XML) • Systems within network built on N-tier technology • Typical use: • Place an order at a supplier system • Problems: • Scalability • Management

23. Challenge - Systems become more and more distributed • Deutsche’s fallacies of networking becomes an issue: • The network is reliable • The latency is zero • Bandwidth is infinite • The network is secure • The topology doesn’t change • There is one administrator • Transport cost is zero • There is one administrator • These issues are not handled by classical architectures such as: • N-tier • Client / Server

24. Network Network Participant Participant Distributed architectures – Participant to Participant protocol • Participant can be anything from a super computer, printer, mobile phone, PDA or car • Participants may be limited with respect to power supply, memory and cpu capacity • Participants will be switched on and off • A participant must advertise its services, and be able to find other participants services • Existing architectures does not support this: • They fail on Deutsche’s fallacies • Dynamic lookup of services • Sun Jini network technology provides a solution: • Dynamic distribution of networked services is built into the language run-time environment • www.jini.org • rio.jini.org • java.sun.com/jini

25. JavaSpaces – an example of a distributed object store • A JavaSpace is defined by a Java interface: • write(Entry tmpl, Transaction txn, Long lease) • read(Entry tmpl, Transaction txn, Long timeout) • readIfExist • take • takeIfExist(Entry tmpl, Transaction txn, Long timeout) • notify(Entry tmpl • snapshot(Entry e) • An entry is a Java object implementing the Entry interface • Class PersonEntry implements Entry, PersonBean { • Public String name; // Space requires public • Public String address: • Public void setName(String name) • Public String getName() • JavaSpace is based on Linda Tuple spaces developed at Yale (Gelerntner)

26. DB Agent DB Agent DB Agent Example of a space based web architecture • The Servlet receives HTTP requests and process these requests. • Business objects are stored as JavaBeans in a JavaSpace, and the servlet will read and write bean objects to and from the space • Behind the space specialized agents listens for specific types of requests in the space and produces valid response objects. • The effect of this architecture is total decoupling of client side from server side. • The space can be located anywhere and neither the servlet nor the agents need to worry about that. • This architecture is an example of a alternative to client/server and N-tier, though the blueprint conforms to an N-tier solution. Web Container Servlet read write take JavaSpace JavaBean Void setX(i:X) X getX()

27. Architectural evolution in terms of generations • N-tier • Distribute applications and services across systems • Requires a tightly controlled network • An extension of the client/server model • CORBA, EJB and DCOM • Network to Network • Systems in different networks can communicate • Systems itself built with N-tier technology • Web services, XML, UDDI, SOAP • Participant to participant • A participant in one network can identify and communicate with a participant located in another network • Jini network technology Participant to Participant Network to Network N-tier Client / Server

28. Summary • Web is similar to IBM’s terminal world of 1974 • Systems Network Architecture • Client/Server and N-tier components requires stable and controlled networks • Deutsche’s fallacies • Understanding round-trip delay and latency is required • Components more rigid than first anticipated • New architectures required for next generation of distributed collaborative systems • Jini Network technology provides a solution • Architectures are critical in today’s software systems • The more complex systems success depends on architecture at both system and software levels.

29. From domain model to code A practical tour based on Java

30. The design process – Building a working system • Decompose system into modules • Maximize cohesion • Minimize coupling • Determine relations between modules • Inheritance • Composition • Identify where flexibility is desirable and where it is not • Determine the form of inter module communication • Remote Procedure Calls • Messaging • Specify module interfaces • Should be well defined • Facilitate independent testing • Improve group communication

31. Characteristics of bad design and their cause • Rigid • hard to change because every change affect the whole system • Fragile • when making a change, unexpected parts of the system fails • Immobile • hard to reuse in other applications because of tight couplings • The main cause of bad design is direct mapping of the domain model • Violating documented design principles • Object oriented languages makes this worse • What about components?

32. Design in practice – Levels • Architectural (system) design: • Scope: Subsystems, Processors, Tasks, Packages, safety & reliability • Patterns: Micro kernel, Rendezvous, Broker, Proxy • Define terminology • Mechanistic design: • Scope: Class collaboration • Patterns: Design Patterns (GOF) and Core J2EE patterns  • Detail design: • Scope: Class, Data and O-R mapping

33. Phases of design, scope and deliveries Source: Doing hard time, Douglas 1999

34. Architectural design – Processors (physical) Processor boundary = network boundary Think of the software layers

35. Architectural design - Tasks • Definition • Separate function that must occur or appear to occur concurrently • Task types: • Event driven • Clock driven • Priority and Critical • Task coordinator • Implementation: • Java Threads • Agents • Message driven beans • Standalone processes • EJB session beans

36. Architectural design – Packages • Packages is a grouping mechanism of functionality • UML has a representation, the same has Ada , C++ and Java • A poor package structure in Java will haunt the system in its lifetime • Separate specification from implementation • Use separate source threes • Package structure defines the architecture Specifications: • no.cellnetwork.marketplace.business.MarketServiceFactory • no.cellnetwork.marketplace.business.UserAccountService Implementation: • no.cellnetwork.marketplace.business.MarketServiceFactoryImpl • no.cellnetwork.marketplace.business.UserAccountServiceImpl

37. Architectural design – Packages and sub-systems Defence system • Group functionality into logical packages • Required to manage complexity • Identify interfaces and package dependencies • Abstract versus concrete packages Commercial system

38. Architectural design – Packages and Layers • User Interface Layer • Responsible for all user interactions • Realized by portal frameworks and to some extent Swing components. • Includes Web services and XML interfaces for communication • Business Service Layer • Responsible for domain specific functions • Realized by JavaBeans,Session Beans, Jini Services and Servlets and other ordinary classes • Data & Integration Layer • Responsible for data access and access to other systems • Implemented in databases (SQL), Entity Beans and Data Access Objects • Asynchronous messaging a part of this layer

39. Architecture – Illustrated • User Interaction Layer • Web, Rich client (swing) and Mobile • User Interaction Layer • Tag libraries a issue • Usability a issue • Information architecture a issue • Business Service Layer • Defined by interfaces and interfaces only. • Interfaces should be network ready. Eg. Throws RemoteException. • Implemented as EJB, Servlet,JavaBean’s • Data & Integration Layer • Defined by interfaces, message standards and database tables. • Agents are self contained processes with a well defined purpose • Agents can also implement domain specific business rules • Message service can be JMS, Corba, JavaSpaces • Data can be local databases or external legacy systems. Communication managed by agents Business Service Layer Business Service Business Service Business Service Data & Integration Layer Access Service Access Service Message Service Agent Agent Data Data Data

40. Mechanistic design • Mechanistic design is concerned with adding and organizing classes to support a particular implementation strategy • Bruce Powel Douglass • Goal: Transform the analysis model into a effective working design • Maximize cohesion • Minimize couplings • Tools: • Separate specifications from implementation • Design patterns (GOF book) • Inheritance and composition • What about EJB’s?

41. Practical design step one – decomposing the domain model

42. ContractService findAll findBySeller findByBuyer OfferService make Find BidService make accept find RequestService make find BidBean getPrice setPrice CarMarketBean setPrice getPrice Contract getPrice getBuyer Identified services and data objects

43. Marketplace services and factory specification

44. Service specification • Specification consists of: • Specification is composed of package and interface • The service throws RemoteException and is implicit networked enabled • Its up to the implementer to decide on distribution or not • Sample code package no.cellnetwork.business.marketplace; import Java.rmi.RemoteException; public interface RequestService { public Collection find(...) throws RemoteException; public void make(..) throws RemoteException; }

45. RequestService – EJB design

46. Service implementation – EJB example Specify EJB specific interfaces package no.cellnetwork.business.marketplace; import javax.ejb.EJBObject; public interface BidServiceRemote extends EJBObject, BidService{} public interface BidServiceHome extends EJBHome { public BidServiceRemote create() throws RemoteException,,; } Implementing the bean package no.cellnetwork.business.marketplace; public class BidServiceBean implements SessionBean, BidService { public Collection find(){} public void make() {} public void accept() {} }

47. Implementing the factory • public RequestService createRequestService() { • RequestServiceRemote remote = null; • InitialContex ctx = new InitialContext(); • try { • Object ref = ctx.lookup("RequestService"); • RequestServiceHome home =(RequestServiceHome)PortableRemoteObject.narrow(ref,RequestServiceHome.class); • remote = home.create(); • } catch (Exception e) { • // throw new MarketException("Could not createRequestService"); • } • return (RequestService)remote; • }

48. Detail design – the last step before code • Scope: • Classes and type safe attributes • Representing complex data structures • Database design and OR mapping • Object oriented databases and Java Data Objects

49. Making attributes type safe • Ada provides this: • Type Missile_Speed_Type is float 0.0..6000.0; • Type Missile_Range_Type is float 0.0..4000.0; • Missile_Speed : Missile_Speed_Type; • Missile_Range : Missile_Range_Type; • Some_Float : Float; • Some_Float := Missile_Range + Missile_Speed; -- Stopped by compiler !! • Java requires class encapsulation: • Lack of operator overloading an issue: • Class Speed_Type ….. • Class Range_Type ……

50. Mapping objects to relational databases • Database on 3’d normal form is good for objects too • No redundancy - performance an issue, use your brain • No internal dependency - unique rows • Database should be designed to support the object model • Relations a result of business methods in objects • Complex queries best done manually (Torque is a tool but performance an issue) • Stored procedure speeds performance • What about entity beans • Think of it as a persistent object • Spann one table, though EJB 2.0 supports foreign key • Small result sets • Consider to use a Data Access Service • Returns valueObjects (JavaBean’s) • Encapsulates your SQL