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An Engineering Approach to Webbased Application Development

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Title: An Engineering Approach to Webbased Application Development


1
An Engineering Approach to Web-based Application
Development
  • Cornelia Boldyreff
  • Distributed Systems Engineering Group,
  • RISE, University of Durham, UK
  • www.dur.ac.uk/cornelia.boldyreff

2
Outline
  • Web Site Development and Maintenance
  • Web Metrics
  • Web Site Evolution
  • Web Management and Design Processes
  • Web Site Engineering

3
Web Site Development and Maintenance
  • Recognition of potential Web maintenance problem
    and very interesting case of software evolution
  • Key paper - Measuring Readability and
    Maintainability of Hyperdocuments, Hatzimanikatis
    et al, JSM, 1995
  • Possibility of working with Richard West and
    colleagues managing UK government Web sites

4
Initial Findings
  • Uneven, largely poor, quality of authorship
  • Badly structured web documents
  • Difficulty in navigating web documents
  • Hypertext structures rapidly become complex as
    the linking of nodes increases
  • Lack of tools for managing Web development and
    maintenance

5
Further Findings
  • Applications on the WWW are often distributed and
    therefore maintained by several
    authors/maintainers
  • Maintenance of WWW applications relies on the
    error logs of each server, complaints from users,
    periodic checks by owners
  • No general consensus of opinion, or standards, on
    what constitutes a good web application
    therefore assessment is difficult

6
Analyzing and Assessing Hyperdocuments
  • Readability Factors
  • Maintainability Factors
  • Effectiveness Factors - Usability
  • Evaluation process in practice needed
  • High level factors needed to be related to low
    level measurable factors
  • Lessons to be learnt from classical software
    engineering, especially software maintenance

7
Key Results
  • Analysis and Assessment of Web documents GQM
    and ISO Product Quality Standard
  • Requirements Studies for Web Site Development and
    Management Support
  • Workbench developed - see www.dur.ac.uk/cornelia.b
    oldyreff/workbench

8
Solving the Broken Link Problem
  • Major effort needed to maintain links and ensure
    their currency
  • Existing solutions involved non-standard
    implementations, e.g. Hyper-G(Hyperwave)
  • Guardian Agent solution implemented using
    standard http and CORBA - employing both eager
    and lazy link update - patented by British Telecom

9
BT Requirements for WWW Maintenance
  • Link management - if documents are relocated,
    links should be redirected automatically to the
    new document location
  • Version control - support re-configuration of
    existing sites with new up-dates
  • Support of team working - several authors should
    be able to work on the same documents without
    interfering with each other

10
Guardian Agents
  • Compatible with WWW
  • Provide on-line maintenance
  • Work in background - transparent to the user
  • Flexible
  • Scalable
  • Configurable

11
Guardian Agents
  • Guardian Agents analyze, monitor and record the
    following information
  • Outgoing and incoming links
  • Who accesses the web application
  • Who changes the web application

12
Determining Success - Web Quality Metrics
  • Apply Goal-Question-Metric
  • Metrics derived from Software Metrics, e.g.
    Complexity measures
  • Tailored Hypertext Metrics, e.g. tree impurity
  • New Web Metrics, e.g. Brays html sincerity
  • Both static and dynamic measures required

13
Software Evolution - Web Evolution
  • Inspired by Lehman classic studies in Software
    Evolution
  • Metrics here used to study changes over time
  • Aim to understand and predict the web evolution
    process
  • Support better, more controlled, web maintenance
    and management

14
Early Metrics
  • Key paper - Measuring Readability and
    Maintainability of Hyperdocuments, Hatzimanikatis
    et al, JSM, 1995
  • Also earlier work by Brown on maintaining
    long-life hypertext, Botafogo et al, and Garzotto
    et al on hypertext quality
  • Brays paper, Measuring the Web, WWW5, 1996

15
Content Metrics
  • Measures to effect editorial control, e.g. spell
    checking, grammar checking, content checking
    (refereeing)
  • Measures to gauge readability, e.g. sentence
    lengths, vocabulary analysis, font analysis
  • Measures to gauge usability, e.g. accessibility
    checking (Bobby - www.cast.org/bobby),
    colour-blindness checking

16
Structural Metrics
  • Metrics derived from Software Metrics
  • Per-document metrics LOC - lines of code, COM -
    lines of comments, NOM - number of modules
    (nodes), number of links (edges), counts of
    various html tags, MVG - McCabes Cyclomatic
    complexity within the documents (for local
    links), fan-in, fan-out, Henry-Kafura/Sheppard
    information flow measure - (fan-infan-out)2
  • per-site metrics Number of documents, totals and
    means of the above measures

17
Web Evolution Studies
  • Structural metrics used
  • Method
  • develop and apply measurements over time
  • identify patterns of change and develop models of
    change
  • test theories against more case studies
  • Fixed intervals of times used instead of release
    dates as in classical software evolution studies

18
WWW as Software-in-the-large
  • Web software evolves and degrades like
    conventional software - all forms of change
    occur. Perfective, adaptive, corrective, and
    preventative maintenance is needed
  • Speculative or Pre-emptive maintenance is also
    needed (e.g. Link Checking)
  • Maintenance may introduce errors - regression
    testing
  • A large manpower commitment is required

19
WWW as Software-in-the-small
  • Hypertext is represented as a graph - compare the
    call graph of traditional programs
  • Links are edges Modules (files) are nodes.
  • Web pages may contain embedded software, e.g.
    cgi, Java, VRML, etc
  • Users execute links
  • Different kinds of links images, frames, etc
  • Referential/organizational links

20
Web Sites Chosen for Study
  • S.T.A. - 20 files (very small)
  • Cartercopters - 60 files (small)
  • Durham University (part) - 641 (medium)
  • Sunderland University (part) - 438 (medium)
  • BBC - thousands
  • BT - thousands

21
SiteSeer and parsley
1 per site
  • Web spider
  • parsley built using UNIX lex and yacc
  • problems of robot exclusion and perturbation
  • other tools used to view and manipulate graphs
    produced

SiteSeer
parsley
parsley
1 per document
22
Early results from studies
  • Simple metrics collected easily
  • Large quantities of data to analyze
  • Index documents easily identifiable -
    characterized by high fan-out (and fan-in) -
    exhibit very high coupling
  • Observed that the overall rate of change of a
    site increased with the size of the site -
    smallest site exhibited no changes during first
    study
  • Growth but never shrinkage!

23
Further Results
  • Recurrent structures emerged from studies of site
    graphs - indices, tours, picture galleries can
    all be identified. Possible basis for further
    research on web design patterns.
  • High link density (links per document) is
    strongly related to the probability of additional
    links being added to the document per unit time.

24
Future Web Metrics Research
  • Research on hypertext and web metrics is in its
    infancy. Existing metrics require better
    interpretation (e.g. mapping from low level
    measures to high level quality factors).
  • A unified measurement programme combining
    structural metrics with content metrics,
    especially usability, is needed.

25
Web Site Classification
  • Web site evolution studies used a 2-D
    classification site size and nature of site
    ownership
  • Others have used size and development focus
    (long-lived, short-lived, one-off applications),
    site type educational, commercial and
    institutional
  • Some metrics may be more relevant to certain
    classes of sites, so determining a web site
    classification is a useful step before further
    metrics research.

26
Proposed Dimensions
  • Size
  • Domain
  • Purpose
  • Functionality
  • Technology
  • Age
  • Rate of Change
  • Evolution Strategy

27
Observations
  • It seems likely that the maintenance process
    evolves with time and as the site grows, e.g. no
    changes, minor corrections, managed re-design,
    multi-developer site, multiple data base driven
    site.
  • Evolution is closely related to usability as
    following Lehmans first law, it can be
    anticipated that a large web application must
    undergo continuous change or it will become
    progressively less useful.

28
Further Observations
  • Measuring and modeling the WWW allows us to study
    its structure and contents, and determine quality
    factors operationally.
  • Classification of Web Sites can give us a better
    insight into appropriate measures to study their
    evolution. One size does not fit all!
  • Studying Web sites and how they change over time,
    gives us insights in web design and maintenance
    processes and their possible improvement.

29
Web Management and Design Processes
  • Early process models developed based on UK
    government web site management practice
  • Hypermedia/Web Development methods and models -
    surveyed and classified
  • Metrics used here to guide research on process
    models for Web Site Engineering

30
Web Process Models
  • Durham Workbench model for Web Maintenance - 1995
  • UK government - CCTA Management Model 1996
  • Survey of Hypermedia Design Methods - 1998
  • Lowe and Halls Hypermedia Development Process
    Model - 1999

31
Early Maintenance Process Model
32
CCTA Management Model
Web page Development
Customer Awareness
Train in Web page development
External Organization
Database of HTML files
Transfer checked Web pages
Get customer for CCTA
CCTA Customer
CGIS Team
Mirror database of HTML files
Develop Web Pages
Check the page
Guidelines for Web page presentation
CGIS Team
33
Hypermedia/Web Development models and methods
Survey
  • Design and Development stages from different
    methods
  • abstracted Hypermedia/Web Development stages
  • Relationship hierarchy of various methods

34
Method Relationship Hierarchy
Hypermedia Design Methods
EORM Lange
HDM Garzotto
OOHM Hendrix
STDT Bichler
HM-Data Maurer
RMM Isakowitz
Semi-formal methods
OOHDM Schwabe
Web Architect Takahashi
Extended RMM
Database Design Techniques
Object Oriented Techniques
35
Stages from Methods
36
Hypermedia Development stages
Feasibility Requirements Analysis
Requirements document
Conceptual Design
Conceptual design diagrams e.g. ER diagrams or
classes, etc
Navigational Design
Nodes and links, navigational diagrams, e.g.
Slices
User Interface Design
Interface and screen diagrams
Conversion Implementation
Finished Product
Testing Maintenance
37
Lowe and Halls Development Process Models
  • found in their book - Hypermedia the Web An
    Engineering Approach
  • Based on Traditional Software Engineering process
    models the Waterfall, Prototyping, Spiral Model.
  • Fullest model includes project planning, risk
    management and project management with overall
    system architecture, system design and
    application partitioning.

38
Web Process Improvement and CMM
  • Process models, methods, plus metrics provide the
    basis for Web Process Improvement
  • Companies need guidance on how best to improve
    their existing Web development and maintenance
    practices
  • Web Usability Engineering is a good starting
    point as it is key when a company is trying to
    attract and keep its Web site customers

39
Web Site Engineering projects
  • Web-SEM project - Establishing Effective Web Site
    Evaluation metrics - building on earlier web
    metrics and evolution studies combined with web
    usability and quality metrics
  • Small projects on web site re-engineering, clone
    detection, web site re-use (web-in-a-box), web
    site life cycle and automating recurrent
    maintenance activities, metrics for web quality
    determination.

40
Improving Basic Web Site and Web Product Design
  • Popularising the concept of web engineering -
    taking a systematic and disciplined approach to
    engineering web applications among small and
    medium enterprises - Business Informatics project
  • Working with the CACDP to migrate all their
    products and services to the WWW, helping them to
    develop a well-defined engineering approach with
    systematic reuse along classic SPI/CMM lines

41
Web Site Engineering
  • Applying and adapting classical Software
    Engineering models, methods and tools to the
    engineering of web-based applications, e.g. web
    pages, web sites, web applications in general.
  • Special case of Distributed System Engineering
  • Closely related to Software Engineering but also
    recognizing important differences, e.g. periodic
    nature of web maintenance, pre-emptive nature of
    maintenance, faster rates of change, larger
    scales of deployment/usage than in classical
    software.

42
Towards Web Site Engineering
  • Well developed models of Web development and
    maintenance processes
  • Web Software Quality Determination
  • Models and Laws of Web-based Software Evolution
  • Support for distributed developers - Computer
    Supported Co-operative Working applied to Web
    Site Engineering

43
Key Points
  • Web developers and maintainers can learn from
    Software Engineering
  • Web metrics can help to evaluate, to describe,
    and to develop new approaches to web engineering
    processes and products
  • Software Engineering can provide a foundation for
    Web Engineering
  • Web Evolution studies provide guidance

44
Software Engineering
Distributed System Engineering
Software Metrics and SPI
Human-Computer Interaction
Hypermedia (Graph) Theory
Usability Metrics
Hypertext Metrics
Hyper-media Design
Web-based Software Engineering
45
References
  • Warren et al, The Evolution of Websites, IWPC99.
  • Warren et al, Characterising Evolution in Web
    Sites Some Case Studies, WSE99.
  • Boldyreff et al, Web-SEM Project Establishing
    Web Site Evaluation Metrics, WSE2000
  • Boldyreff et al, Establishing a Measurement
    Programme for the World Wide Web, SAINT01
  • Boldyreff et al, Towards the Engineering of
    Commercial Web Based Applications, SSGRR01
  • Kyaws technical report - Survey of Hypermedia
    Design Methods, CS-3-98
  • Lavery, Designing Web Site Usability, and other
    links on www.dur.ac.uk/janet.lavery
  • see Donkins webpages at www.dur.ac.uk/j.m.donkin
  • Boldyreff and Kewish, Reverse Engineering to
    Achieve Maintainable WWW Sites, WCRE01
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