Hypermedia APIs for Sensor Data

A pragmatic approach tothe Web of Things

Mobiquitous 2014

Spencer RussellJoe Paradiso

MIT Media Lab

Responsive Environments Group

Big Picture

• global scale
• not meant to replace low-power protocols
• build on web technologies
• leverage existing infrastructure and talent

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• Assume a plurality of low-level device protocols

• abstract them from clients

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• allowing intermediaries
• handle caching, authentication, and encryption

• so this is in many ways what is common now
• app servers not speaking same language
• no standard way for them to connect to each other
• still better because of the layers

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• present resource relations
• affordances(creating a device, sending a command)
• currently using JSON-HAL, but JSON-LD looks nice as well
• Going to spend a little time here, as it's important!

• now with hyperlinks

• And now lets focus on the application servers

• But say we have a lot more application servers

• so now we have something that looks a lot like the early-90s web
• now what came along in 1994 to help consumers find what they wanted

• the web is a substrate for innovation, an ecosystem we can grow new services on top of

• now that we have all these links, what do they mean?...

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• Support interoperability via shared vocabularies
• specifically focus on vocabulary of relation names and data types
• terms identified with URIs
• lightweight to extend

• Need vocab for relation types, data types
• HAL gives nice way to tie relations to URLs to identify and describe
• some (esp. search engines) are already using Schema.org data types

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• enabled by hyperlinks and shared vocabulary
• Provide semantic relationships
• Probably not necessary to tie in to Upper Ontology
• don't require full Semantic Web buy-in from developers

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• use familiar standards (HTTP, JSON, and WebSockets)
• no specialized tooling or libraries

{
    "firstName": "Spencer",
    "lastName": "Russell"
}

• raw JSON doesn't give us QUITE enough
• we still need hyperlinks and shared vocabulary

{
    "_links": {
        "self": { "href": "/api/user/837" },
        "address": { "href": "/api/address/938" }
    },
    "firstName": "Spencer",
    "lastName": "Russell"
}

• just JSON with links
• has a mechanism for the relation name to be a URL, but I won't go into it here
• this gives us everything we need

Low-Level Protocol Diversity

Layered Architecture

Hyperlinks

Shared Vocabularies

Semantic Relations

Familiar Standards, Minimal Tooling

Pub/Sub

• allow clients to subscribe to push updates

• use links to tell clients when streams are available

Implementation

• reference implementation is in progress, but in use now
• basically everything except the shared vocabularies

• python
• django and flask
• postgres

490 Devices

2257 Sensors

Over 240,000,000 measurements

6 applications

• devices using a variety of protocols
• applications: (2x unity, 2x glass, javascript web, SOOFA)
• common protocols are a lot easier in unique or niche environments (e.g. Unity)

Live

http://chain-api.media.mit.edu

Open Source

https://github.com/ssfrr/chain-api

Spencer Russell

sfr@media.mit.edu

@ssfrr

github.com/ssfrr

Security

• admittedly security isn't a focus of my research
• brand-new security schemes scare me