Most of your applications need to store data somewhere and probably relational databases like MySQL, PostgreSQL etc.. are the most commonly used for this purpose.
Passing from a relational database to TerminusDB requires some effort and a shift in your state of mind, but it can be done relatively fast. In this tutorial we’ll show you some parallels with how TerminusDB handles tasks compared to relational databases and the goals you can achieve with TerminusDB that are difficult to do with others databases.
if you have never used TerminusDB before, this article includes everything you need to get started with TerminusDB. My First TerminusDB Graph Visualisation — Bike Share Data.
Note: We are assuming you have knowledge of relational database concepts and you already know how to write a simple sql (Structured Query Language) statement.
In our examples we use the collection of data about the bike journeys between stations in Washington D.C., USA.
The CSV data used this tutorial is available at https://terminusdb.com/t/data/bike_tutorial.csv
As you already know SQL is a standard language for accessing and manipulating relational databases.
A conceptual database schema is a description of a database structure, data types, and the constraints on the database.
We can consider a relational database as a collection, or a set of tables. For storing our dataset we need three tables: bikes, stations and journeys. Here the complete schema
Each table consists of rows and columns, in very simple way the columns specify the type of data, where the rows contain the actual data itself and the tables are related to each other.
Let’s see a fragment of schema:
CREATE TABLE `journeys` ( `idJourney` int(11) NOT NULL AUTO_INCREMENT, `bikeId` int(11) NOT NULL, ......), FOREIGN KEY (bikeId) REFERENCES bikes(idBike),
Here our logical relationship from tables: The bikeId column is a FOREIGN KEY to the table bikes (idBike column).
In terminusDB instead of tables we have documents, so for our dataset we need to create three different documents: Station, Journey and Bicycle, every document have a label and a description and is identified by an unique URL. In our documents we have properties to describe the type of data and the documents are related to each other as interlinked concepts.
An example of relationship between documents written in woql.js
WOQL.when(true).and( WOQL.doctype("Station") .label("Bike Station") .description("A station where bicycles are deposited"), WOQL.doctype("Bicycle") .label("Bicycle"), WOQL.doctype("Journey") .label("Journey") .property("journey_bicycle", "Bicycle").label("Bicycle Used") .property("start_time", "dateTime") .....)
In the Journey document the range data type of the journey_bicycle property (ObjectProperty) is the Bicycle document.
What we wish to do now is load the data from our .csv file inside our relational database, but which road map follows to save the integrity of the data relationship, you can use an external tool or you can implement your sql statement.
You could write an sql statement like this to import the csv file inside bikes or stations
LOAD DATA LOCAL INFILE 'bike_tutorial.csv' INTO TABLE bikes FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' IGNORE 1 LINES (@col1,@col2,@col3,@col4,@col5,@col6,@col7,@col8) set bikeNumber=@col8;
But populating the journeys table could be more complicated because you have to get bikeId and stationId from the preview table, maybe you can use a temporary table to load all the CSV data and after, you can move the data from the temporary table to bikes, stations, journeys.
In TerminusDB we have a very cleaner solution to import csv files into the database, with a data integrity check for any newly imported records.
const csv = WOQL.get( WOQL.as("Start station","v:Start_Station") .as("End station", "v:End_Station") ...... .as("End station number", "v:End_ID") .as("Bike number", "v:Bike") .as("Member type", "v:Member_Type") ).remote("https://terminusdb.com/t/data/bike_tutorial.csv")
We refer the first row of our file that contain the column headers in our variables, for example the field “Bike number” refers the variable “v:Bike”
//Clean data for insert const wrangles = [ WOQL.typecast("v:Duration", "xsd:integer", "v:Duration_Cast"), WOQL.typecast("v:Bike", "xsd:string", "v:Bike_Label"), WOQL.typecast("v:Start_Time", "xsd:dateTime", "v:ST_Cast"), WOQL.typecast("v:End_Time", "xsd:dateTime", "v:ET_Cast"), WOQL.typecast("v:Start_Station", "xsd:string", "v:SS_Label"), WOQL.typecast("v:End_Station", "xsd:string", "v:ES_Label"), WOQL.idgen("doc:Journey",["v:Start_ID","v:Start_Time","v:Bike"],"v:Journey_ID"), WOQL.idgen("doc:Station",["v:Start_ID"],"v:Start_Station_URL"), WOQL.idgen("doc:Station",["v:End_ID"],"v:End_Station_URL"), WOQL.idgen("doc:Bicycle",["v:Bike_Label"],"v:Bike_URL"), WOQL.concat("v:Start_ID - v:End_ID @ v:Start_Time","v:J_Label"), WOQL.concat("Bike v:Bike from v:Start_Station to v:End_Station at v:Start_Time until v:End_Time","v:Journey_Description") ];
We cast (WOQL.typecast(a,b,c) method) the variable “V:Bike” as string (“xsd:string”) and refer it in a new variable “V:Bike_Label”
We create an unique id (WOQL.idgen(a,b,c) to every document. Example for “doc:Bicycle” document we create an id from the “v:Bike_Label” and refer it in the “v:Bike_Url”
const inserts = WOQL.and( WOQL.insert("v:Journey_ID", "Journey").label("v:J_Label") .description("v:Journey_Description") ..... .property("journey_bicycle", "v:Bike_URL"), ..... WOQL.insert("v:Bike_URL", "Bicycle") .label("v:Bike_Label") );
Now we can insert the data inside our database. We create a “Bicycle” document for every “v:Bike_URL” value and we link this value inside the “journey_bicycle” property in Journey document. Our relationship link between document has been created ❗ In this article the complete example My First TerminusDB Graph Visualisation — Bike Share Data.
Query the Data
Now, how we write our query for getting all the information about the bike journeys.
Here an Sql example
SELECT journeys.startTime, journeys.endTime, bikes.bikeNumber, journeys.memberType, journeys.duration, startStation.address as startStation, startStation.stationNumber as startStationNumber, endStation.address as endStation, endStation.stationNumber as endStationNumber FROM journeys INNER JOIN stations as startStation ON journeys.startStation = startStation.idStation INNER JOIN stations as endStation ON journeys.endStation = endStation.idStation INNER JOIN bikes ON journeys.bikeId=bikes.idbike;
Let’s see the TerminusDB woql query
WOQL.select("v:Bike_Number", "v:End_Time", "v:Start_Time","v:Start_Label", "v:End_Label","v:Duration").and( WOQL.triple("v:Journey", "type", "scm:Journey"), WOQL.triple("v:Journey", "duration", "v:Duration"), WOQL.triple("v:Journey", "end_time", "v:End_Time"), WOQL.triple("v:Journey", "start_time", "v:Start_Time"), WOQL.triple("v:Journey", "start_station", "v:Start"), WOQL.opt().triple("v:Start", "label", "v:Start_Label"), WOQL.triple("v:Journey", "end_station", "v:End"), WOQL.opt().triple("v:End", "label", "v:End_Label"), WOQL.triple("v:Journey", "journey_bicycle", "v:Bike"), WOQL.opt().triple("v:Bike", "label", "v:Bike_Number") )
Could you guess that the TerminusDB schema model is an ontology (OWL) ? It is extremely difficult to express queries against graph structured ontology, but with our query language we are shielded from the complexity of interfacing with the ontology keeping the power of an ontology data model. ❗ You can not query an ontology with sql.
Let’s keep to practise ❗