Linked Data is still largely unknown, or misunderstood and undervalued. Often, people find it simply too difficult. So I keep looking for new ways to make Linked Data more accessible. And with some success. In my training courses so far over 60% of the participants had no IT background. I hope even to increase this percentage in the future.
What seems to be most challenging is writing SPARQL queries. The specification is written for IT people. There are some great courses and books but they also target people with some or more IT experience. If anything, that scares the rest and keeps SPARQL away from the masses.
I keep learning what is challenging. A recurring problem – and an unexpected one – is the concept of variable.
What is a variable in SPARQL? Just a placeholder. But how can you imagine a placeholder? It’s abstract. We have no way of grasping abstract things unless we associate them with something physical and concrete. It’s difficult to imagine time, but once we draw it in space it gets easier. We can’t picture furniture, but we have no problem with chair.
The other issue is how a SPARQL query looks. While working with SPARQL helps to understand how a knowledge graph works, a SPARQL query doesn’t look like one. It is like with symbols in mathematics. “5 doesn’t look like five, while ||||| is five”. The problem with SPARQL is similar:
You want to query knowledge graph.
You want to learn new things.
But your query doesn’t look like knowledge graph.
It looks like lines of strings.
So, how to handle together the problems with grasping variables and with the look of SPARQL?
My suggestion is to imagine every SPARQL query as a graph of linked buckets and balls.
Variables are placeholders but abstract. We need a physical container1The idea of using containers is very powerful. The whole arythmetics and alegbra can be done using only the concept of container as demonstrated by William Bricken. to fill with things. We need buckets. And nodes are like balls. So, think of running2“Running” is also a metaphore and what it stands for can be communicated more gracefully. And that’s important. As you know, language shapes the way we think. a query as filling buckets with balls.
A graph pattern then will look like this:
A bucket ?A should be filled with those balls which have a relation R to ball B.
But it looks nicer when we abbreviate it like this:
This is a graph pattern in Buckets’n’Balls notation. The direction of the relation R is not shown but it’s always from left to right.
The process of writing and running a SPARQL query would then go through the following steps: Continue reading