Task-Oriented, Policy Driven Business Requirements for Web ...

Task-Oriented, Policy Driven Business Requirements for Web ...

Task-Oriented Business Requirements Elicitation for Web Services Stephen Gorton IST-FET IST-2005-16004 Department of Computer Science, University of Leicester, University Road, Leicester LE1 7RH Web Service Architecture Composition often the top layer; R eeq q u iu r ei m tse n t s R r een m Composition and orchestration still a blur! Exportable service Software service Software Composite Composite service service Little regard for a more abstract requirements layer.

service service service service UDDI, WSDL, etc. UDDI, WSDL, etc. HTTP, HTTPS, SMTP, etc. HTTP, HTTPS, SMTP, etc. BCTCS 05/04/06 Task-Oriented, Policy Driven Business Req uirements for Web Services 2 Current Solutions 1 Approach 1: Composition as Requirements BPEL: DAML-S Code snippets taken from Milanovic and Malek: Current Solutions for Web Service Composition. IEEE Internet Computing, Nov/Dec 04 BCTCS 05/04/06

Task-Oriented, Policy Driven Business Req uirements for Web Services 3 Current Solutions 2 Approach 2: Specialised Requirements Language BPMN: B A + + C UML: B A C BCTCS 05/04/06 Task-Oriented, Policy Driven Business Req uirements for Web Services 4 Wedding Example Business goal g = plan wedding; Broken down into objectives (composite tasks): ct1 = plan pre-wedding celebrations;

ct2 = plan preparations; ct3 = plan legalities; ct4 = plan ceremony; ct5 = plan post-ceremony celebrations; ct6 = plan honeymoon. Tasks are arranged according to result timeline, not according to execution timeline! e.g. ceremony and post-ceremony celebrations often planned in parallel. Policies: The entire event should not cost more than 10k; The ceremony and post-ceremony celebrations should be on the same day; The honeymoon should be booked through a known and trusted travel agency. BCTCS 05/04/06

Task-Oriented, Policy Driven Business Req uirements for Web Services 5 Booking the Honeymoon 1 Flows: start Control runs from start to finish; Solid lines indicate control flow routes; A task is executed when control reaches it; Control proceeds when the task has finished. t1 t2 Flow Split: FS: in -> OUT; Control proceeds down each output simultaneously; No limit on number of output

flows; Parallel split workflow pattern t3 2 t4 Conditional Merge: CM: IN -> out; Forces synchronisation; Mandatory and optional flows; Specifies minimum number of flows; Discriminator workflow pattern. BCTCS 05/04/06 t5 t6 t7 2 Task-Oriented, Policy Driven Business Req uirements for Web Services 6

Booking the Honeymoon 2 Strict Preference: SP: in -> out; Input is a set of pairs {t, n} t is a task; n is a priority rating; t8 New workflow pattern. Flow Merge: FM: IN -> out; Incoming set of control flows contains only one active flow; No synchronisation issue; (Multiple) Merge workflow pattern. t9 t11 t10

t12 p1 c1 Random Choice: RC: in -> out; All tasks invoked; When a first gets to a commit, all others are cancelled; New workflow pattern. BCTCS 05/04/06 Task-Oriented, Policy Driven Business Req uirements for Web Services end 7 Other Notation Flow Junction Operator:

fx FJ: in -> {out1, out2}; Left output is primary; Output flow chosen according to a test; Exclusive choice workflow pattern. test fx.1 fx.2 Bounded cycles allowed: For both composite and atomic tasks; Can be modelled with flow junction and flow merge. (since we only allow one control flow input, a flow merge function should be used). BCTCS 05/04/06 ti n Task-Oriented, Policy Driven Business Req uirements for Web Services 8

Summary Current notations not appropriate: UML has some merits but does not support many workflow patterns; BPMN is the nearest to a complete solution; None allow for the expression of all requirements. A simple graphical notation: Describing process flows; Scope for core and non-core (non-functional) requirements; Offers the context in which policies are used. Further work: Workflow patterns (data and resource patterns); Policies and policy framework at the business level; A workbench. BCTCS 05/04/06 Task-Oriented, Policy Driven Business Req uirements for Web Services 9 Thank you. Any Questions? BCTCS 05/04/06 Task-Oriented, Policy Driven Business Req uirements for Web Services 10

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