1. 590ES1 Design of Plant Care System Mike Swift Steve Swanson Stefan Bjarni Sigurdsson

2. 590ES2 Scenario You buy a plant You buy an automatic watering / feeding system You buy automatic plant lights You buy plant monitoring system You subscribe to www.burpee.com You want this all to work together

3. 590ES3 Design Principles Components to system: –Base objects: hardware devices with software interfaces Sensors Actuators –Services –Service Manager –Data store

4. 590ES4 Base objects: Sensors (a hardware device) –Occasionally produces a measurement –Knows how to talk to store, or has a wrapper –If sensor can be controlled, it has an actuator to control it Poke it to make a measurement Schedule future measurements Actuators (also a hardware device) –Make something happen –Knows how to receive commands, or has a wrapper

5. 590ES5 Base Objects Description of component is downloaded from a URL –What is the interface used? –What is the precision / characteristics? –What are the measurement units? –What is the class of device (e.g. temperature / moisture / sound / light / plant )

6. 590ES6 Services Services are software They can provide simple services: –Data aggregation / interpretation Average temperature dTemp/dt – temperature change –Actuator aggregation Lighting a whole area Thermostat –Publishing information from one data store to another

7. 590ES7 Services (2) They can provide high level functionality –Read from sensors / write to actuators –Access outside information sources –Example: Plant care system

8. 590ES8 Service Management The Service manager is responsible for: –Discovery –Adding services (join) –Binding: creating communication channels between services –Dependency management for service invocation –Authentication of services May store services in a tuple space

9. 590ES9 Data Store Shared data is kept in the store Store contains XML documents with: –Type information –Creator information The store can remember everything The store implements access control There is a 1-1 relationship with service managers.

10. 590ES10 Data Store (2) There may be multiple data stores –One per room –One per apartment Data stores may be aggregated Services may publish information upwards –Has to be an explicit choice to release information –May only release aggregated information E.g. daily average temperature, not instantaneous temp.

11. 590ES11 Data Store (3) Store may generate events –Notify services that a condition has occurred New services available Existing services failed New data available

12. 590ES12 Assumptions Everything communicates through interfaces or data sets There exists standards for common concepts, such as: –Location –Temperature –Time –precision

13. 590ES13 Step by Step Data store and service manager are already installed Devices are brought into house –Acquire network address (DHCP?) –Register with service manager Send URL & UID to service manager Description downloaded from net May periodically send aliveness information, or respond to probes –Sensors may start producing data immediately

14. 590ES14 Step by step (2) Customer purchases service from www.burpee.com www.burpee.com Service is registered in service manager –Queries for components related to plants –Download additional services needed for operation Eg: thermostat services

15. 590ES15 Service Installation Services register dependencies in service manager –What other services are needed? E.g. aggregator service for a particular sensor / set of sensors –Each service that is depended on registers its dependencies If measurements are needed, a service may need to schedule an actuator to force a measurement

16. 590ES16 Service Installation (2) What if dependencies can’t be satisfied? –Reduce quality of service: Reduce precision Reduce service –Don’t water plants –Don’t adjust lighting –Don’t monitor plants individually

17. 590ES17 Operation Sensors periodically make measurements Aggregator services are notified by the data store of new data and convert data to more abstract information High level service polls / is notified of high-level information, makes a decision Propagates action to actuators

18. 590ES18 Fault Tolerance An aggregator service may hide the fault of a low level sensor –Aggregate around the missing data –Change precision of measurements Decreased location accuracy Decreased time accuracy Decreased value accuracy If fault is not recoverable, log to error log –Error handling service monitors error log, determines what can be fixed –Pass up to next dependent service

19. 590ES19 Security Security depends on authentication Authentication depends on consensus knowledge –Secret key (on bar code?) –Public key/private key pair –Location Local devices are not on internet – they go through a proxy/firewall/intermediary All local communication is encrypted to prevent wiretaps

20. 590ES20 Security (2) User has to make some decisions –www.burpee.com is allowed to access plant datawww.burpee.com –Needs policy specifications for class of devices / usage E.g. plant care Climate control –Or, allow user prompt for each service (not)

21. 590ES21 Security (3) Information in data store is purely local –Not accessible from WWW –Local services may upload information to WWW –Any other info must be explicitly published

22. 590ES22 Service Conflicts May have two services with conflicting commands –E.g. two plants near each other with conflicting temperature needs There can be several resolution methods –Average the commands –Prioritize the commands E.g. fire sprinkler takes precedence over cactus –Time division multiplexing –Propagate conflict up, let higher level service change policies

23. 590ES23 Diagram Data Store Service Mgr. TempMoistBright HeaterWaterFood Plant Care Avg. Temp Set Moist

24. 590ES24 Diagram Explained Dotted lines show virtual communication Triangles are sensors Lightning is actuators Ovals are services Arrows show information flow –From sensors –To actuators