Query the Data Delivery Network

The easiest way to query any data on Splitgraph is via the "Data Delivery Network" (DDN). The DDN is a single endpoint that speaks the PostgreSQL wire protocol. Any Splitgraph user can connect to it at data.splitgraph.com:5432 and query any version of over 40,000 datasets that are hosted or proxied by Splitgraph.

For example, you can query the multimodal_intelligent_traffic_signal_systems table in this repository, by referencing it like:

"datahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288:latest"."multimodal_intelligent_traffic_signal_systems"

or in a full query, like:

SELECT
    ":id", -- Socrata column ID
    "msgid", -- The DSRC Message ID is a data element used in each message to define which type of message follows from the message set defined by this Standard. This data element is always the first value inside the message and is used to tell the receiving application how to interpret the remaining bytes (i.e. what message structure has been used). This value is enumerated and the values and corresponding meaning are as follows: 0 – Reserved, 1 – A La Carte Message (ACM), 2 – Basic Safety Message (BSM – heartbeat message), 3 – Basic Safety Message Verbose (BSM used for testing only), 4 – Common Safety Request (CSR), 5 – Emergency Vehicle Alert (EVA), 6 – Intersection Collision Alert (ICA), 7 – Map Data (MAP, GID, intersections), 8 – nmea Corrections (NMEA), 9 – probe Data Management (PDM), 10 – probe Vehicle Data (PVD), 11 – Roadside Alert (RSA), 12 – rtcm Corrections (RTCM), 13 – Signal Phase And Timing Message (SPAT), 14 – Signal Request Message (SRM), 15 – Signal Status Message (SSM), 16 – Traveler Information (TIM) 
    "speed", -- This field contains the vehicle speed in km/hr.
    "elev", -- This field contains the current elevation, in feet, of vehicle according to GPS.
    "msgcnt", -- This data element is used to provide a sequence number within a stream of messages from the same sender with the hexadecimal numeral system. 
    "location", -- NA
    "location_state",
    "location_city",
    "location_zip",
    ":@computed_region_28hd_vqqn",
    "tempid", -- This field contains the ID (number) of the device (or vehicle) that transmits a BSM.
    "location_address",
    "latitude", -- This field contains the current latitude, in degrees, of the vehicle.
    "secmark", -- This field SecMark is a simple value consisting of integer values from zero to 59900 representing the milliseconds of a wall clock minute.  
    "type", -- This field contains the type of the collected data.
    "timestamp", -- This field contains the time in deciseconds with an Epoch time format.
    "source", -- NA
    "longitude", -- This field contains the current longitude, in degrees, of the vehicle.
    "heading" -- This field contains the vehicle heading/direction, in degrees.
FROM
    "datahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288:latest"."multimodal_intelligent_traffic_signal_systems"
LIMIT 100;

Connecting to the DDN is easy. All you need is an existing SQL client that can connect to Postgres. As long as you have a SQL client ready, you'll be able to query datahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288 with SQL in under 60 seconds.

This repository is an "external" repository. That means it's hosted elsewhere, in this case at datahub.transportation.gov. When you querydatahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288:latest on the DDN, we "mount" the repository using the socrata mount handler. The mount handler proxies your SQL query to the upstream data source, translating it from SQL to the relevant language (in this case SoQL).

We also cache query responses on the DDN, but we run the DDN on multiple nodes so a CACHE_HIT is only guaranteed for subsequent queries that land on the same node.

Query Your Local Engine

bash -c "$(curl -sL https://github.com/splitgraph/splitgraph/releases/latest/download/install.sh)"

Splitgraph Cloud is built around Splitgraph Core (GitHub), which includes a local Splitgraph Engine packaged as a Docker image. Splitgraph Cloud is basically a scaled-up version of that local Engine. When you query the Data Delivery Network or the REST API, we mount the relevant datasets in an Engine on our servers and execute your query on it.

It's possible to run this engine locally. You'll need a Mac, Windows or Linux system to install sgr, and a Docker installation to run the engine. You don't need to know how to actually use Docker; sgrcan manage the image, container and volume for you.

There are a few ways to ingest data into the local engine.

For external repositories (like this repository), the Splitgraph Engine can "mount" upstream data sources by using sgr mount. This feature is built around Postgres Foreign Data Wrappers (FDW). You can write custom "mount handlers" for any upstream data source. For an example, we blogged about making a custom mount handler for HackerNews stories.

For hosted datasets, where the author has pushed Splitgraph Images to the repository, you can "clone" and/or "checkout" the data using sgr cloneand sgr checkout.

Mounting Data

This repository is an external repository. It's not hosted by Splitgraph. It is hosted by datahub.transportation.gov, and Splitgraph indexes it. This means it is not an actual Splitgraph image, so you cannot use sgr clone to get the data. Instead, you can use the socrata adapter with the sgr mount command. Then, if you want, you can import the data and turn it into a Splitgraph image that others can clone.

First, install Splitgraph if you haven't already.

Mount the table with sgr mount

sgr mount socrata \
  "datahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288" \
  --handler-options '{
    "domain": "datahub.transportation.gov",
    "tables": {
        "multimodal_intelligent_traffic_signal_systems": "5tsh-j288"
    }
}'

That's it! Now you can query the data in the mounted table like any other Postgres table.

Query the data with your existing tools

Once you've loaded the data into your local Splitgraph engine, you can query it with any of your existing tools. As far as they're concerned, datahub-transportation-gov/multimodal-intelligent-traffic-signal-systems-5tsh-j288 is just another Postgres schema.