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Implementing SensorThings API for OpenIoT #30

Closed hylkevds closed 10 years ago

hylkevds commented 10 years ago

I'm planning to implement the SensorThings API on top of the OpenIoT platform and I've got some questions before I start coding:

Since it's inspired by OData, does the demo server actually use an OData server library, or is it a custom implementation?

Where/how does the SensorThings API differ from OData?

Do you intend to open-source the demo server implementation?

liangsteve commented 10 years ago

Hi Hylke,

It is great to know you will be implementing SensorThings!! Awesome!!

Here are my answers / views, and I hope they can capture the SensorThings API and the SWG's view. I also include the OGC mail list in the reply.

1: The demo server isn't using Odata server library. It's an implementation from scratch.

2: What's the difference between SensorThings and Odata? Big question and good timing. Here is my long answer. And hopefully it's useful for anyone who is following this list as well as the OGC mail list.

Background: At the beginning (back in last 2012 and 2013), we were thinking to design SensorThings on top of Odata. And one of the benefits is implementers may directly use Odata libraries to implement SensorThings API. At the time, we referenced to Odata 3.0 (which is not an OASIS standard). However, during last year Odata was evolving from 3.0 to 4.0 (in OASIS). Odata officially became an OASIS standard earlier this year (yes, v4.0 is the first official standard). And today's Odata 4.0 is quite different from Odata 3.0. Odata 3.0 were the version we were referencing at the time. Odata 4.0 becomes more "powerful" now (what I want to say is more complex now :p). And in my opinion, if we want to be 100% compliant to Odata, SensorThings will become too complicated and heavy. And I think most of the SWG members will agree with me that an IoT standards needs to be simple and easy.

And in Crystal TC (March 2014), the SWG decides to consider looking into JSON-LD, as JSON-LD is a web standard on the rise. With some further research, Odata 4.0 and JSON-LD has some conflicts (details here http://www.w3.org/2011/rdf-wg/track/issues/162) and that makes things more interesting now. And in both Crystal TC and Geneva TC, the SWG also decides to look into MQTT as pub/sub is a core IoT use case and members are requesting pub/sub functions. So we looked into MQTT and OdataŠ.ahŠ.we opened another can of worms. Odata is using a unique URL convention. E.g., http://rootURL/Datastreams(1) rather than http://rootURL/Datastreams/1/. And the Odata URL convention makes it difficult to integrate with MQTT. So we have some design decisions to make now. But I still believe some Odata concepts are very useful and innovative, and we should keep them. To make the answer short, in my opinion, SensorThings API will follow some aspects from Odata but will not claim that it is Odata compliant. And in fact, SensorThings API is pretty different from today's Odata 4.0.

The important similarities include:

  1. The concept of the collection of entities http://docs.oasis-open.org/odata/odata/v4.0/os/part1-protocol/odata-v4.0-os- part1-protocol.html#_Toc372793657
  2. Relationships from one entity to another can be represented as navigation properties. (http://docs.oasis-open.org/odata/odata/v4.0/os/part1-protocol/odata-v4.0-os -part1-protocol.html#_Toc372793592)
  3. We use the same query options specified by Odata such as server-side paging ($select, $expand, $top, $skip, etc.) and queries (eq, nq, gt, gt, lt, etc.) More here: http://docs.oasis-open.org/odata/odata/v4.0/os/part1-protocol/odata-v4.0-os- part1-protocol.html#_Toc372793681

3: Yes. We will open source the implementation. But I cannot confirm timeline at the moment though (it's part of our research projects, so it involves funders and stake-holders).

Cheers,

Steve

Dr. Steve H.L. Liang, Ph.D. P.Eng. Associate Professor AITF-Microsoft Industry Chair in Open Sensor Web Department of Geomatics Engineering Schulich School of Engineering University of Calgary 2500 University Drive NW Calgary, Alberta T2N 1N4 Tel: (403)220-4703 Fax: (403)284-1980 http://sensorweb.geomatics.ucalgary.ca http://www.geocens.ca Twitter: @steveliang

From: Hylke van der Schaaf notifications@github.com Reply-To: OGC-IoT/ogc-iot-api <reply+i-37250123-2b9548f5997329eef215316e13fa5928fa0db6e0-4602885@reply.git hub.com> Date: Monday, 7 July, 2014 2:56 AM To: OGC-IoT/ogc-iot-api ogc-iot-api@noreply.github.com Subject: [ogc-iot-api] Implementing SensorThings API for OpenIoT (#30)

I'm planning to implement the SensorThings API on top of the OpenIoT platform and I've got some questions before I start coding:

Since it's inspired by OData, does the demo server actually use an OData server library, or is it a custom implementation?

Where/how does the SensorThings API differ from OData?

Do you intend to open-source the demo server implementation?

‹ Reply to this email directly or view it on GitHub https://github.com/OGC-IoT/ogc-iot-api/issues/30 .

hylkevds commented 10 years ago

Thank you for that in-depth reply. Quite a bit longer than expected :)

It's good to know that OData is currently only used as an inspiration, that means I won't have to look into any OData libraries. OData does indeed have many interesting ideas in it.

liangsteve commented 10 years ago

No problem. BTW, since you are an OGC member, did you subscribe to the OGC SWE-IoT mailing list? If not, it would be a good idea to do so.