Declarative Interface for In-network Actuation on Wireless - - PowerPoint PPT Presentation

Declarative Interface for In-network Actuation on Wireless Sensor-Actuator Networks

Asanka Sayakkara M.D.J.S Goonetillake Kasun De Zoysa

Sustainable Computing Research Group (SCoRe), University of Colombo School of Computing, Sri Lanka.

Outline

• Wireless sensor networks (WSN)
• Database abstraction for WSN
• Cougar and TinyDB
• Wireless sensor actuator networks (WSAN)
• TinyDB for WSAN
• Greenhouse scenario
• Issues in declarative interface for WSAN
• Solution approach
• Evaluation
• Discussion
• Conclusion

Wireless Sensor Networks (WSN)

• Low powered devices.
• Wireless communication.
• Limited computing resources.
• Built-in sensors.

Database Abstraction for WSN

• Hides the complex network details and provide a familiar

interface.

Cougar and TinyDB

• Cougar from Cornell University

➔ The pioneering work in the domain. ➔ In network query processing

• TinyDB as a joint work from MIT, UCB and Intel Research

➔ First successful implementation. ➔ Widely used in real world applications

SELECT nodeid, light FROM sensors SAMPLE PERIOD 1 FOR 10;

Specify Data Sampling Rate

Wireless Sensor Actuator Networks (WSAN)

• Having just sensors in the network is not enough.
• New requirements for controlling the deployed environment in

addition to monitoring.

• Actuators are attached to the nodes in a network.
• Some nodes may have just sensors, some may have just

actuators and some may carry both sensors and actuators.

TinyDB for WSAN

• Special keywords to specify which action should be performed.
• Calls to low level system functions.

SELECT nodeid,temperature FROM sensors WHERE temperature > 25 OUTPUT ACTION sprinkler-on() SAMPLE PERIOD 10s

The function to be Called Specify Data Sampling Rate

The Greenhouse Scenario

• A greenhouse with wireless sensors and actuators.

(Only the components Of our concern are shown)

The Greenhouse Scenario (continued)

SELECT nodeid FROM sensors WHERE (nodeid=5 OR nodeid=7) AND temperature>35 AND humidity>45 ONCE; SELECT nodeid FROM sensors WHERE nodeid=9 OUTPUT ACTION air-cooler-on() ONCE; SELECT nodeid FROM sensors WHERE nodeid=15 OUTPUT ACTION screen-ctrl-on() ONCE; SELECT nodeid FROM sensors WHERE nodeid=23 OUTPUT ACTION sprinkler-on() ONCE;

Issues In Declarative Interface For WSAN

• 1. Violation of declarative nature.
• 2. Inefficiency in complex actuation tasks.

Solution Approach

• Actuators were not the concern of TinyDB developers.
• Data acquisition query syntax has been extended to support

actuators using a new keyword.

• To solve declarative nature violations we need better query

syntax for actuation tasks.

Virtual Data Table

nodeid temperature humidity 1 25 40 2 28 39 3 27 NULL 4 NULL 41 nodeid temperature humidity air-cooler sprinker 1 25 40 NULL NULL 2 28 39

• ff
• ff

3 27 NULL

• n

NULL 4 NULL 41

• ff
• n

Traditional Sensors table Enhanced table With sensors And actuators

Actuation By Updates

• Actuator attributes in the table are alterable.
• We can update actuator attributes by using traditional update

queries. UPDATE sensors SET air_cooler=’on’ WHERE nodeid=2 AND temperature>20 ONCE;

Still we need to specify sampling rate

Actuation By Updates (continued)

• Multiple nodes can involve for a single actuation task.
• Alias can be used to perform such tasks.

UPDATE sensors AS sen, sensors AS act SET act.air_cooler=’on’ WHERE (act.nodeid=4 OR act.nodeid=2) AND (sen.nodeid=1 AND sen.temperature>20) ONCE;

Such as Greenhouse scenario

Query Execution

Evaluating Declarative Nature

• Randomly selected a group of 10 students who have an

average knowledge on acquisitional queries.

• Provided them with different actuation scenarios and asked

them to write SQL queries to perform those actuation tasks in both existing and the suggested approaches.

• Collected feedback from them regarding how they found writing

queries for actuation tasks in both approaches.

Evaluating Declarative Nature (continued)

• Each person participated in the survey considers the existing

approach of performing actuation tasks has unnecessary syntax restrictions.

• All the participants consider the modified virtual table with

actuators as attributes is more convenient to handle than the

• ld table.
• Most of them have struggled to write queries using the existing

syntax for the greenhouse scenario.

Actuation Time

• Actuation time Vs Number of fields in a query.

Discussion

• Having NULL values in the virtual table doesn't add any overhead to

the query execution cost.

• Adding a list of functions to TinyDB query syntax can reduce the

multiple query usage to some extent. But still declarative nature violation remains.

• Node mobility should be seriously considered in the future.
• Require efficient ways to execute UPDATE queries in the network.

Conclusion

• Considering actuators as a part of the data model in the

database abstraction is more convenient.

• UPDATE queries can be used to perform actuation tasks in the

network.

• Executing actuation queries in the network needs more

research to handle node movements, node failures, etc.