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Class Exercise I: Use Cases

Deborah McGuinness and Joanne Luciano

with Peter Fox and Li Ding

CSCI-6962-01

Week 4, September 27, 2010

Presented by Peter Fox

Contents

• Use case introduction

• Elements of use case documentation

• Class exercise – use cases in real-time

• Assignment reading: Ontology Tool Summary, Pellet, OWL-S, SAWSDL, Wine Agent

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Semantic Web Methodology and Technology Development Process

• Establish and improve a well-defined methodology vision for Semantic Technology based application development

• Leverage controlled vocabularies, et c.

Use Case

Small Team, mixed skills

Analysis

Adopt Technology Approach

Leverage Technology

Infrastructure

Rapid Prototype

Open World: Evolve, Iterate,

Redesign, Redeploy

Use Tools

Science/Expert Review & Iteration

Develop model/

ontology

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Use Case

• A use case is a collection of possible sequences of interactions between the system under discussion and its Users (or Actors), relating to a particular goal.

• The collection of Use Cases should define all

system behavior relevant to the actors to assure them that their goals will be carried out properly.

• Any system behavior that is irrelevant to the actors should not be included in the use cases.

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Use Case

• is a prose description of a system's behavior when interacting with the outside world.

• is a technique for capturing functional requirements of business systems and, potentially, of an IT system to support the business system.

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Use Case

• Must be documented (or it is useless)• Should be implemented (or it is not well

scoped)• Is used to identify: objects ~ resources,

processes, roles (aka actors), requirements, etc.

• Should iterate with experts on wording and details at least once

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Roles and skill-sets needed

• Facilitator *** (usual key skills, knows method)• Domain experts (literate, knows resources; data,

applications, tools, etc.)• Modelers (to extract objects)• Software engineers (architecture, technology)• Scribe (to write everything down)• The social aspect is key - it is a team effort

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Roles and skill-sets

• Facilitator – you may not be ready to play this role but you will need to ‘pretend’

• Engage some domain experts (they are literate, know the resources; data, applications, tools, etc. and you can share this role)

• You will be the modeler (to extract objects, triples)• You may play the role of a software engineer

(architecture, technology) but you can also ask someone for help with this

• Write as much as you can down• Be prepared to be social - it is a team effort

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Note

• Your roles and what is/ is not expected of you

• Be prepared to draw on the white board• Keep your scoping in mind as you are

proceeding– Identify objects, processes, actors/roles,

organizations (or nouns, verbs, adjectives)

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Use Case Examples

• Make a collection of *any data format* model run datasets available for internet access with web browsing to find suitable data and access to the data via Matlab.

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Use Case Examples:

• Provide browse and quick look access to a broad variety of climate, weather and ocean data.

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Use Case Examples:

• Install an OPeNDAP Hyrax server with THREDDS cataloging on the front-end to support netCDF and HDF4 data sets on the back-end and allow aggregation based on NcML and authentication of user access

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Use Case Examples:

• Provide high-performance data transfer of specific climate model data products into the climate diagnostics and analysis tool (CDAT) for analysis, independent of their storage format, organization or location on the internet

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Use Case Examples:

• A US 9th grade teacher is preparing a lesson plan aimed at getting students to learn more about the ‘northern lights’, addressing NSES content standards in earth science. The teacher wants the students to learn the scientific terminology, where the phenomena occurs and retrieve some data or graphics for a recent occurrence. The goal of the lesson plan is the engage students, using authentic data from the aurora, as part of an inquiry-based program.

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Elements of a Use Case

• http://wiki.esipfed.org/index.php/SolutionsUseCase_Template

• Start with the Plain Language Description– Short Definition– Purpose– Describe a scenario of expected use– Definition of Success

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Short Definition• Define the use case in plain sentences• Wherever possible avoid specifying technical

solutions or implementation choices• Concentrate on the application aspects of the

intended scenario • Also note when the use case may be applicable

to more than one application area

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Purpose• A plain language description of

– why this use case exists,– what the problem is to be solved,– what a successful outcome, and – what the impact may be.

• Often termed the ‘business case’

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Scenario of expected use

• A verbose (more detailed) description of one instance of a problem to be solved– what resources are generally needed (if known)– what a successful outcome and impact may be– who might be expected to do the work or provide the

resources and – who might be expected to benefit from the work

• List any performance or metric requirements for this use case and any other other considerations that a user would expect.

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Definition of Success

• Quick test that would show whether or not the case is working as described.

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At this stage

• Use case modelers should have a good sense of what the use case goal is.

• They proceed on to the next stage to extract details.• They may contact other team members, e.g.

domain experts, one-on-one for additional information.

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Formal Use Case Description

• Use Case Identification

• Revision Information• Definition• Successful Outcomes• Failure Outcomes

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General Diagrams

• Schematic of Use case

• How to draw diagrams:– Stick figures for actors (person or computer)

– Boxes to denote resources– Arrows to denote process flow– Concept maps are a useful tool

Diagrams

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Use Case Examples:

• A US 9th grade teacher is preparing a lesson plan aimed at getting students to learn more about the ‘northern lights’, addressing NSES content standards in earth science. The teacher wants the students to learn the scientific terminology, where the phenomena occurs and retrieve some data or graphics for a recent occurrence. The goal of the lesson plan is the engage students, using authentic data from the aurora, as part of an inquiry-based program.

Developed for NASA TIWG

Schematic

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Use Case Elaboration

• Actors– Primary Actors– Other Actors

• Preconditions• Postconditions• Normal Flow (Process Model)

• Alternative Flows• Special Functional Requirements

• Extension Points

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Diagrams

• Use Case Diagram• State Diagram• Activity Diagram• Other Diagrams

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Non-functional requirements

• Performance• Reliability• Scalability• Usability• Security• Other Non-functional Requirements

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Alternate form

• Use case name• Summary• Activity diagram• Preconditions in tabular form• Triggers• Basic flow• Alternate flow• Post conditions

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Preconditions - data/model

Data Resource

Type Characteristics Description Owner Source System

(dataset name)

Remote,

In situ,

Etc.

e.g. – no cloud cover

Short description of the dataset, possibly including rationale of the usage characteristics

USGS, ESA, etc.

Name of the participating system which supports discovery and access

Model Owner Description Consumes Frequency Source System

(model name)

Organization that offers the model

Short description of the model

List of data consumed How often the model runs

Name of the participating system which offers access to the model

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Preconditions - event/application

Event Owner Description Relevant subscription

Source System

(Event name)

Organization that offers the event

Short description of the event List of subscriptions (and owners)

Name of the participating system which offers this event

Application/

DSS

Owner Description Source System

(Application name)

Organization that offers the Application

Short description of the application Name of the participating system which offers this event

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Which format to use?

• Short (in document) format for:– Exploratory phase of a project where you want

to collect a lot of use cases – An example for others to use– Including in a proposal– In an assignment (hint)

• Long (on wiki) format for:– Detailed documentation of the use case– Life cycle documentation for implementation– Asynchronous/ collaborative development– Part of a group assignment (another hint)

Scoping

• Focus initially on:• Core functionality• What it takes to implement the use case, resist

early generalizations• May (will) have to iterate on use case and

requirements

• Acknowledge other important issues such as:• Required vs. optional• Non-functional requirements• Available personnel (skills) and resources

Actors• The initial analysis will often have many

human actors• Begin to see where these can be replaced

with machine actors – may require additional encoding

• If you are doing this in a team, take steps to ensure that actors know their role and what inputs, outputs and preconditions are expected of them

• Often, you may be able to ‘run’ the use case (really the model) before you build anything 34

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Actors

• Real people (round heads) and computers (block heads)

• E.g. Data provider, end-user, data manager, alert service

• Primary – initiate (act on)• Secondary – respond (acted upon)

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What’s a pre-condition?

• defines all the conditions that must be true (i.e., describes the state of the system) for the trigger to meaningfully cause the initiation of the use case.

Preconditions• Often the preconditions are very syntactic and

you may not understand how they fit in the implementation

• Some level of modeling of these preconditions may be required (often this will not be in your first pass encoding which focuses on the main process flow, goal, description, etc.)

• Beware of using another entities data and services: policies, access rights, registration, and ‘cost’

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What’s a post-condition?

• describes what the change in state of the system will be after the use case completes. Post-conditions are guaranteed to be true when the use case ends.

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Success scenarios

• A re-statement of how the use case via its flows and actors and resources results in achieving the result

• Describe artifacts produced

• Describe impacts and metric values

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Failure scenarios

• A statement of how the use case via its flows and actors and resources did not result in achieving the result

• Describe role of actors in failure

• Describe role of resources in failure

• Describe what artifacts were and were not produced

• Describe impacts of failure and any metric values

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Normal (process) flows

• A basis step of (usually) distinct steps that result when the use case is triggers (commences)

• Steps are often separated by actor intervention or represent modular parts of the flow (can encapsulate activities)

• Can have loops

• Should end with the final goal achieved

Process flow• Each element in the process flow usually denotes

a distinct stage in what will need to be implemented

• Often, actors mediate the process flow• Consider the activity diagram (and often a state

diagram) as a means to turn the written process flow into a visual one that your experts can review

• Make sure the artifacts and services have an entry in the resources section

• This is often the time you may do some searching (no, not soul searching – web searching…) 42

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Alternate (process) flows• Variations from the main flow, often invoked

by valid but non-usual (or rules)• Activity diagrams are useful in representing

this part of the document• Do not usually represent exceptions/ error

flows• Can often help to identify general patterns in

the use case via similarities with the normal flow

• While many are possible, usually only include one - illustrative

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Functional/ non-functional

• (from Wikipedia): requirements which specify criteria that can be used to judge the operation of a system, rather than specific behaviors.

• This should be contrasted with functional requirements that specify specific behavior or functions.

• In general, functional requirements define what a system is supposed to do whereas non-functional requirements define how a system is supposed to be.

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Functional/ non-functional• (from Wikipedia): Non-functional requirements are

often called qualities of a system. Other terms for non-functional requirements are "constraints", "quality attributes", "quality goals" and "quality of service requirements".

• Qualities, (non-functional requirements), can be divided into two main categories.– Execution qualities, such as security and usability, are

observable at run time.– Evolution qualities, such as testability, maintainability,

extensibility and scalability, are embodied in the static structure of the software system.

Artifacts• Add artifacts that the use case generates to the

resources list in the table• It is often useful to record which artifacts are critical

and which are of secondary importance• Be thinking of provenance and the way these were

produced, i.e. what went into them and produce suitable metadata or annotations

• Engage the actors to determine the names of these artifacts and who should have responsibility for them (usually you want the actors to have responsibility for evolution)

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Reviewing the resources• Apart from the artifacts and actor resources, you

may find gaps• Define/ find the authoritative sources for data,

information, metadata, configuration• Your encodings can also be a resource, make it a

first class citizen, e.g. on the web give it a namespace and a URI

• Sometimes, a test-bed with local data is very useful as you start the implementation process, i.e. pull the data, maybe even implement their service (database, etc.)

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When someone asks: “What is your use case”?

• Treat it like your ‘elevator pitch’

• Know them, especially the ones you have implemented

• Tell them how you used it to develop a solution FOR use

If you have not developed one

• Try reverse engineering

• Start with a personal example

e.g. balancing your checkbook

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Resources

• http://alistair.cockburn.us/index.php/Use_cases,_ten_years_later• http://www.digilife.be/quickreferences/pt/functional%20requirements%20and%20use

%20cases.pdf• http://alistair.cockburn.us/index.php/Resources_for_writing_use_cases

• http://alistair.cockburn.us/Usecasesintheoryandpractice180.ppt• http://alistair.cockburn.us/Agileusecases1dy.ppt• http://alistair.cockburn.us/index.php/Structuring_use_cases_with_goals• http://www.foruse.com/publications/bibliographies/usecases.htm• http://en.wikipedia.org/wiki/Use_case• http://www.ddj.com/dept/architect/184414701

• Omnigraffle (Mac) www.omnigroup.com/applications/omnigraffle/ or

• Cmap http://cmap.ihmc.us/• wiki template

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Notes

• Tactics - users are alien to this process• Facilitator is the key role• The social aspect - brief everyone on their role and

what is expected of them (and what is not)• UML4US (arrow, box, stick fig., text)• Learn how to identify objects, processes,

actors/roles, organizations (or nouns, verbs, adjectives)

• Functional versus non-functional requirements and how to tell the difference

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Developing a service ontology

• Use case: find and display in the same projection, sea surface temperature and land surface temperature from a global climate model.

• Find and display in the same projection, sea surface temperature and land surface temperature from a global climate model.

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Developing a service ontology• Use case: find and display in the same projection,

sea surface temperature and land surface temperature from a global climate model.– Name:– Goal:– Summary:– Actors:– Preconditions:– Triggers:– Normal flow:– Alternate flow:– Post condition:– Activity diagram:– Notes

• Find and display in the same projection, sea surface temperature and land surface temperature from a global climate model.

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Reminder: Services• Ontologies of services, provides:

– What does the service provide for prospective clients? The answer to this question is given in the "profile," which is used to advertise the service. To capture this perspective, each instance of the class Service presents a ServiceProfile.

– How is it used? The answer to this question is given in the "process model." This perspective is captured by the ServiceModel class. Instances of the class Service use the property describedBy to refer to the service's ServiceModel.

– How does one interact with it? The answer to this question is given in the "grounding." A grounding provides the needed details about transport protocols. Instances of the class Service have a supports property referring to a ServiceGrounding.

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Service ontology• Climate model is a model• Model has domain• Climate Model has component representation• Land surface is-a component representation• Ocean is-a component representation• Sea surface is part of ocean• Model has spatial representation (and temporal)• Spatial representation has dimensions• Latitude-longitude is a horizontal spatial representation• Displaced pole is a horizontal spatial representation• Ocean model has displaced pole representation• Land surface model has latitude-longitude representation• Lambert conformal is a geographic spatial representation• Reprojection is a transform between spatial representation• ….

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Service ontology• A sea surface

model has grid representation displaced pole and land surface model has grid representation latitude-longitude and both must be transformed to Lambert conformal for display

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Summary• Use cases are a powerful tool for

implementing real semantic e-science applications based on what someone needs to DO!

• Use case should drive the functional requirements of both your ontology and how you ‘build’ one

• Small team, mixed skills: starting to learn this is the nature of your next assignment

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Assignments for Week 4

• Assignment 2: Use-case Driven Knowledge Encoding Part I (Part II is class presentation, in Class 6, due TUESDAY Oct. 12. 1pm ET)

• Reading: Ontology Tool Summary, Pellet, OWL-S, SAWSDL, Wine Agent

• Note: Use file name convention on all files and in the subject line of any assiciated email

Assignment 2• Use-case Driven Knowledge Encoding Part I:

– Develop a use case, ‘on your own’ – to do this you may engage domain experts and other team members.

– You will perform the analysis, ontology modeling and knowledge encoding using the methods and tools you have learned to date and document them.

– You may leverage an existing knowledge base and/or ontologies making it clear what you used, modified and created yourself.

– You will also ask and answer questions about the encoding.

• You will present your use case, using the document format, in class and answer questions. 60