iTasks interactive workflow tasks for the WEB ___________ WORK IN PROGRESS

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i-Tasks-interactive workflow tasksfor the
WEB___________ WORK IN PROGRESS
Rinus Plasmeijer - Peter Achten University of
Nijmegen www.cs.ru.nl/clean
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Overview of the talk

• challenge STW project demand driven
  workflows
• simple approach iTasks workflows based on
  i-Data
• iData
• iTasks
• Conclusions

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Previous work on Graphical Editor Components

• Can we use generic programming techniques to
  generate interactive desktop applications ?
• Yes Graphical Editor Components (IFL '03, PADL
  '04, APLAS '04).
• For any (higher order) type,an editor for values
  of that type can be constructed automatically

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Previous work on Graphical Editor Components

• Can we use generic programming techniques to
  generate interactive desktop applications ?
• Yes Graphical Editor Components (IFL '03, PADL
  '04, APLAS '04).
• For any (higher order) type,an editor for values
  of that type can be constructed automatically
• Can we use generic programming techniques to
  generate interactive web forms ?
• Yes i-Data (FLOPS '06, IFL '05, IFL 06).

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Previous work on Graphical Editor Components

• Can we use generic programming techniques to
  generate interactive desktop applications ?
• Yes Graphical Editor Components (IFL '03, PADL
  '04, APLAS '04).
• For any (higher order) type,an editor for values
  of that type can be constructed automatically
• Can we use generic programming techniques to
  generate interactive web forms ?
• Yes i-Data (FLOPS '06, IFL '05, IFL 06).
• Can we use generic programming techniques to
  generate interactive multi-user workflow systems
  for the web ?
• Yes i-Tasks

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i-Data Interactive Data
An i-Data is a persistent typed object it lives
longer then the application.
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One function to create an i-Data object of any
type

• mkEdit (Init, FormId d) ? HSt ? (Form d,
  HSt) iData d
• Init
• Init Set // Get or Set current value
  
• FormId d
• initval d // value
• , id String // unique web form id
• , mode Mode // Edit, Submit, Display,
  NoForm
• , lifespan Lifespan // Page, Session, File,
  Database
• , storage StorageFormat // String, Dynamic
• HSt // Unique (abstract) data type
• Form d
• changed Bool // has the user edited the
  form ?
• , value d // current value in data domain
  (feel)
• , form BodyTag // html code
  representing view domain (look)

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Example 1 An editor for an integer value

• example hst
• (idata, hst) mkEdit (Init, nFormId myform
  initVal) hst
• mkHtml Txt Editor Example
• , Br
• , BodyTag idata.form
• hst
• initVal Int
• initVal createDefault

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Example 2 An editor for a list of integers

• example hst
• (idata,hst) mkEdit (Init, nFormId myform
  initVal) hst
• mkHtml Txt Editor Example
• , Br
• , BodyTag idata.form
• hst
• initVal Int
• initVal createDefault

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Example 3 An editor for a record structure

• example hst
• (idata,hst) mkEdit (Init, nFormId myform
  initVal) hst
• mkHtml Txt Editor Example
• , Br
• , BodyTag idata.form
• hst
• initVal Person
• initVal createDefault
• Person name String
• , street String
• , number Int
• , zipCode String
• , town String
• derive gForm Person gUpd Person gPrint Person
  gParse Person gerda Person

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Example 4 An editor for a list of records

• example hst
• (idata,hst) mkEdit (Init, nFormId myform
  initVal) hst
• mkHtml Txt Editor Example
• , Br
• , BodyTag idata.form
• hst
• initVal Person
• initVal createDefault
• Person name String
• , street String
• , number Int
• , zipCode String
• , town String

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Example 4 A user defined editor for a list of
records

• example hst
• (idata,hst) listEdit (Init, nFormId myform
  initVal) hst
• mkHtml Txt Editor Example
• , Br
• , BodyTag idata.form
• hst
• initVal Person
• initVal createDefault
• Person name String
• , street String
• , number Int
• , zipCode String
• , town String

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Example Clean's CD shop

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Conclusions iData

• Nice
• High-level easy-to-read specification of
  complicated web forms
• Many low level things are handled automatically
• dealing with interaction over the web
• storage and retrieval in pages, files, databases
• Good separation between model and view
• Specialisation possible that allows to redefine
  any view of any type
• Also multi-user applications easy to realize
• Nice, clear relative simple implementation based
  on generic functions
• One function does it all !

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Sequence of numbers

• sequenceIData hst
• (done1, idata1, hst) myEdit task1" initVal
  hst
• (done2, idata2, hst) myEdit task2" initVal
  hst
• mkHtml "Solution using iData without iTasks"
• BodyTag idata1.form
• , if done1 (BodyTag idata2.form) EmptyBody
• , if done2 (BodyTag Txt "
• ,Hr
• ,toHtml (idata1.value idata2.value))
  EmptyBody
• hst
• where
• myEdit String a HSt ? (Bool, Form a, HSt)
  iData a

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Conclusions iData

• Not so nice
• good in event-driven applications, bad in
  application-driven workflows
• no support for easy definition of such
  workflows
• one single i-Data application is re-started on
  each event
• persistent state editor used to remember and
  control the workflow
• one has to think about prompting and what to show
  or not
• programmer has to invent new unique names for
  iData forms

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iTask approach

• Study Workflow Patterns (Van der Aalst, ter
  Hofstede, Kiepuszewski, Barros)
• pruducts Staffware, Cosa, InConcert, Eastman
  Software, FLOWer, Domino Workflow, Meteor,
  Mobile, MQSeries, Forte Conductor,Verve, Visual
  WorkFlo, Changengine, I-Flow, SAP R/3 Workflow
• patterns sequence, recursion, exclusive choice,
  multiple choice, split/merge (parallel or,
  parallel and, discriminator), ...
• All Workflow Patterns can straightforwardly be
  implemented
• For each pattern define a combinator on top of
  iData
• Composition by using monadic operators / Cleans
  unique state handling
• Form names are generated automatically in a
  systematic way
• Remember evaluation path of the tasks
• iTasks
• are typed (most workflow systems are not)
• and have all the advantages of iData (highly
  reusable)

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Sequence of numbers, iTask, monadic state

• sequenceITaskM (Task a) iData a a
• sequenceITaskM
• STask "Set" initVal
• gtgt \v1 -gt STask "Set" initVal
• gtgt \v2 -gt Txt "", Hr
• !gtgt returnTask (v1 v2)

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Sequence of numbers, iTask, explicite unique state

• sequenceITask (Task a) iData a a
• sequenceITask mytask
• where
• mytask tst
• (v1,tst) STask "Set" initVal tst
• (v2,tst) STask "Set" initVal tst
• tst returnF Txt "", Hr tst
• returnTask (v1 v2) tst

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Sequence of numbers, iTask, multi-user

• sequenceITaskMU (Task a) iData a a
• sequenceITaskMU
• (1,"number") _at_ STask "Set" initVal
• gtgt \v1 -gt (2,"number") _at_ STask "Set" initVal
• gtgt \v2 -gt Txt "", Hr
• !gtgt returnTask (v1 v2)

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Recursion

• repeatTask (Task a) -gt (Task a) iData a
• repeatTask task
• task
• gtgt mkTask (repeatTask task)
• example
• repeatTask CoffeeMachine

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Coffeemachine (1/2)

• CoffeeMachine Task (String, Int)
• CoffeeMachine
• Txt "Choose product", Br, Br
• ?gtgt CTask_button
• ("Coffee 100", returnV (100,"Coffee"))
• , ("Cappucino 150", returnV
  (150,"Cappucino"))
• , ("Tee 50", returnV (50, "Tee"))
• , ("Choclate 100", returnV
  (100,"Choclate"))
• gtgt \(toPay, product) -gt Txt ("Chosen product
  " lt product), Br, Br
• ?gtgt getCoins (toPay, 0)
• gtgt \(cancel, returnMoney)
• -gt let nproduct if cancel
  "Cancelled" product in
• Txt ("product " lt nproduct lt ",
• returned money " lt returnMoney), Br,
  Br
• ?gtgt STask_button "Thanks" (returnV Void)
• gtgt returnV (nproduct, returnMoney)

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Coffeemachine (2/2)

• getCoins (Int, Int) -gt Task (Bool, Int)
• getCoins (toPay, paid)
• Txt ("To pay " lt toPay), Br, Br
• ?gtgt PCTask2
• ( CTask_button (toString i lt " cts",
  returnV (False, i))
• \\ i lt- 5,10,20,50,100,200
• , STask_button "Cancel" (returnV (True, 0))
• )
• gtgt \(cancel, coin) -gt handleCoin (cancel,
  coin)
• where
• handleCoin (cancel, coin)
• cancel returnV (True, paid)
• toPay - coin gt 0 mkTask (getCoins (toPay -
  coin, paid coin))
• otherwise returnV (False, coin - toPay)

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Review Task (1/3)

• ReviewState Approved Cancelled
  NeedsRework TextArea Draft
• taskToReview Int (Task a, a, ReviewState) -gt
  Task (a, ReviewState) iData a
• taskToReview reviewer (task, value, review)
• task value
• gtgt \value -gt reviewer _at_ reviewTask value
• gtgt \review -gt Txt ("Reviewer " lt reviewer
  lt " says "), toHtml review, Br
• ?gtgt STask "OK" Void
• gtgt case review of
• (NeedsRework _) -gt mkTask (taskToReview
  reviewer (task, value, review))
• else -gt returnV (value, review)

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Review Task (2/3)

• reviewTask a -gt Task ReviewState iData a
• reviewTask value,
• toHtml value, Br, Br
• ?gtgt CTask_button
• ("Rework", STask "Done"
  (NeedsRework initVal) ltlt_at_ Submit)
• , ("Approved", returnV Approved)
• , ("Cancel", returnV Cancelled)

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Review Task (3/3)

• QForm toComp String
• , startDate HtmlDate
• , endDate HtmlDate
• , estimatedHours Int
• , description TextArea
• , price Real
• Quotation Task (QForm, ReviewState)
• Quotation taskToReview 1 (mytask, initVal,
  initVal)
• mytask form Txt "Fill in Form", Br, Br
• ?gtgt STask "TaskDone" form ltlt_at_ Submit

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Conclusions iTasks

• Nice intuitive notation
• All "standard" workflows patterns offered
• Workflow diagrams can straightforwardly be
  translated to iTasks code
• Typed workflows,Typed input
• iData based very high re-usability of code
• Simple implementation where evaluation order of
  tasks is remembered using iData
• One application serves multiple users