SCXML Overview. Jim Barnett. Genesys

Transcription

1 SCXML Overview Jim Barnett Genesys

2 Multimodal Applications Are: Unpredictable Don t know what user will do next Procedural languages a bad choice Event processing is the paradigm Stateful What does cancel mean?

3 Multimodal Applications (2) Sub-Stateful Check-out : approve cart, select address, payment type, and shipping Cross-Stateful I want this <click> This is Not a Simple Event Loop JavaScript + HTML will get ugly in a hurry

4 State Chart XML A State Machine Language Based on work of David Harel (Harel State Charts) Related to UML state machine diagrams Good For Reactive Systems Event driven Statefull Event order not predictable.

5 Basic State Machine Concepts States, events, transitions Example: A Shopping Cart States: shopping, checkout Event: tocheckout, toshopping If you re in the shopping state and get the tocheckout event, go to the checkout state If you re in the checkout state and get the toshopping event, go to the shopping state

6 <scxml initial= shopping > <state id= shopping > <transition event= tocheckout target= checkout /> <state id= checkout > <transition event= toshopping target= shopping /> </scxml>

7 Harel Extensions. 1 Data model Example: shopping cart When you get the additem event Update the cartvalue variable with the value of the item that is added Data model is pluggable Specification defines JScript and XPath models

8 <scxml initial= shopping > <datamodel> <data id= cartvalue expr= 0 /> </datamodel> <state id= shopping > <transition event= tocheckout target= checkout /> <transition event= additem > <assign location= cartvalue expr= cartvalue + _event.itemvalue /> </transition> <state id= checkout > <transition event= toshopping target= shopping /> </scxml>

9 Harel Extensions. 2 Conditions on transitions Example: in the shopping state When you get the tocheckout event If cartvalue > $100 go to goldcheckout Otherwise go to regularcheckout

10 <scxml initial= shopping > <datamodel> <data id= cartvalue expr= 0 /> </datamodel> <state id= shopping > <transition event= tocheckout cond= cartvalue > 100 target= goldcheckout /> <transition event= tocheckout target= regularcheckout /> <transition event= additem > <assign location= cartvalue expr= cartvalue + _event.itemvalue /> </transition> <state id= goldcheckout > <transition event= toshopping target= shopping /> <state id= regularcheckout > <transition event= toshopping target= shopping /> </scxml>

11 Harel Extensions. 3 Executable content Example: no shipping charges for goldcheckout Example: send data to reporting server when checkout is done Some Executable content is built in Platforms may add their own

12 <state id= goldcheckout > <onentry> <assign location= shippingfee expr= 0 /> </onentry> <transition event= toshopping target= shopping /> <transition event= checkoutdone target= Finished > <send target= reportingserver namelist= shoppingcart; /> </transition> <onexit> <ext:freecheckoutresources/> </onexit>

13 Compound (Nested) States Example: shipping an order Consists of: checking inventory, pulling the items, updating the inventory, packaging the items and sending them to the shipping dock At any point the order can be cancelled Parent State: inshipping Can be target of a transition Can contain transitions Substates: checkinventory, pullitems, updateinventory, packageitems, sendtodock

14 <state id= inshipping > <transition event= cancelorder target= rollbackorder /> <state id= checkinventory> <transition event= inventorycheckdone cond= _event.checkresult= success target= pullitems /> <transition event= inventorycheckdone target= waitforinventory /> <state id= waitforinventory > <transition event= inventoryarrived target= checkinventory /> <state id= pullitems../> <state id= updateinventory./> <state id= packageitems./> <state id= sendtodock />

15 Parallel States Example: multimodal interface Audio states: user is speaking user is listening, Visual states: user is browsing, user is entering text, Can be in any audio state and any visual state Audio and visual modalities may operate separately BUT: A) They share a data model B) They see each other s events C) They can see each other s state

16 <parallel id= shoppingandinterfaces > <state id= shopping /> <state id= audiointerface > <state id= userspeaking /> <state id= userlistening /> <state id= graphicalinterface > <state id= userbrowsing /> <state id= userenteringtext > <transition event= utterance./> </parallel>

17 Summary Multimodal logic can be complex SCXML can represent complex logic Declaratively Precisely Concisely

18 More Information SCXML Last Call Draft Open Source Implementations github.com/touffy/jsscxml