Programming for beginners: Your First SPARQL Queries in Blazegraph

Now that we've explored the Blazegraph Workbench, let's do something more interesting: query a graph.

To keep things simple, we'll build a tiny Avengers knowledge graph and use it to learn how the Query tab works.

Don't worry if you don't understand every detail yet. The goal here is simply to become comfortable running SPARQL queries and interpreting the results.

Step 1: Load Some Avengers Data

Open the Update tab and insert the following RDF data:

Avengers.turtle

PREFIX : <http://example.org/marvel/>

# Teams

:Avengers a :Team ;
    :name "Avengers" .

:Guardians_of_the_Galaxy a :Team ;
    :name "Guardians of the Galaxy" .

# Heroes

:Iron_Man a :Superhero ;
    :name "Iron Man" .

:Captain_America a :Superhero ;
    :name "Captain America" .

:Thor a :Superhero ;
    :name "Thor" .

:Hulk a :Superhero ;
    :name "Hulk" .

:Black_Widow a :Superhero ;
    :name "Black Widow" .

:Star_Lord a :Superhero ;
    :name "Star-Lord" .

# People

:Tony_Stark a :Person ;
    :name "Tony Stark" ;
    :alias :Iron_Man ;
    :memberOf :Avengers ;
    :portrayedBy :Robert_Downey_Jr .

:Steve_Rogers a :Person ;
    :name "Steve Rogers" ;
    :alias :Captain_America ;
    :memberOf :Avengers ;
    :portrayedBy :Chris_Evans .

:Bruce_Banner a :Person ;
    :name "Bruce Banner" ;
    :alias :Hulk ;
    :memberOf :Avengers ;
    :portrayedBy :Mark_Ruffalo .

:Natasha_Romanoff a :Person ;
    :name "Natasha Romanoff" ;
    :alias :Black_Widow ;
    :memberOf :Avengers ;
    :portrayedBy :Scarlett_Johansson .

:Peter_Quill a :Person ;
    :name "Peter Quill" ;
    :alias :Star_Lord ;
    :memberOf :Guardians_of_the_Galaxy ;
    :portrayedBy :Chris_Pratt .

# Actors

:Robert_Downey_Jr a :Actor ;
    :name "Robert Downey Jr." .

:Chris_Evans a :Actor ;
    :name "Chris Evans" .

:Mark_Ruffalo a :Actor ;
    :name "Mark Ruffalo" .

:Scarlett_Johansson a :Actor ;
    :name "Scarlett Johansson" .

:Chris_Pratt a :Actor ;
    :name "Chris Pratt" .

# Villains

:Thanos a :Villain ;
    :name "Thanos" .

:Loki a :Villain ;
    :name "Loki" .

# Relationships

:Avengers :foughtAgainst :Thanos .
:Avengers :foughtAgainst :Loki .

:Guardians_of_the_Galaxy :foughtAgainst :Thanos .

:Iron_Man :friendOf :Captain_America .
:Thor :friendOf :Hulk .

# Movies

:Avengers_Endgame a :Movie ;
    :title "Avengers: Endgame" ;
    :releasedIn 2019 .

:Infinity_War a :Movie ;
    :title "Avengers: Infinity War" ;
    :releasedIn 2018 .

:Tony_Stark :appearsIn :Infinity_War ;
             :appearsIn :Avengers_Endgame .

:Steve_Rogers :appearsIn :Infinity_War ;
               :appearsIn :Avengers_Endgame .

:Thanos :appearsIn :Infinity_War ;
         :appearsIn :Avengers_Endgame .

Select the type as ‘RDF Data’ and format a Turtle, and click on Update button to insert the data.

Understanding Your First RDF Turtle File

a. What is PREFIX?

The first line is:

PREFIX : <http://example.org/marvel/>

This declares a namespace. Think of it as a shortcut. Without the prefix declaration, we'd have to write following line, every time we wanted to refer to the Avengers.

<http://example.org/marvel/Avengers>

That would become very tedious. Instead, we declare:

PREFIX : <http://example.org/marvel/>

and then simply write:

:Avengers

The colon (:) means, use the default namespace defined above.

:Avengers is shorthand for <http://example.org/marvel/Avengers>
:Team is shorthand for <http://example.org/marvel/Team>
:name is shorthand for <http://example.org/marvel/name>

b. What is the Comment?

This line "# Teams" is a comment. Anything after a hash symbol (#) is ignored by RDF parsers. Comments are useful for organizing RDF files and helping humans understand the data.

c. Understanding the First Triple

Now let's look at:

:Avengers a :Team ;
    :name "Avengers" .

This describes the Avengers.

:Avengers is the subject. The subject is the thing we're talking about.

c.1 What Does a Mean?

This is probably the most confusing part for beginners. The keyword "a" is a special Turtle shortcut.

It means "rdf:type", So

:Avengers a :Team

is exactly the same as

:Avengers rdf:type :Team

And in plain English it means "Avengers is a Team".

c.2 What Does :name Mean?

The next line is:

:name "Avengers"

Here :name is the predicate (relationship) and "Avengers" is the object (value).

In plain English, Avengers has the name "Avengers".

c.3 Why Is There a Semicolon (;)?

Notice this:

:Avengers a :Team ;
    :name "Avengers" .

This is actually shorthand. Without the semicolon, we'd write:

:Avengers a :Team .
:Avengers :name "Avengers" .

Notice how :Avengers is repeated. Since both triples have the same subject, Turtle allows us to write:

:Avengers a :Team ;
    :name "Avengers" .

The semicolon means:

"Keep using the same subject."

c.4 Why Is There a Period (.)?

Every RDF triple ends with a dot (.), the period means "this statement is complete". It's similar to the full stop at the end of an English sentence.

Step 2: Sparql Examples

This Marvel RDF dataset contains:

· Classes (:Person, :Actor, :Movie, :Team)

· Relationships (:memberOf, :alias, :portrayedBy)

· Literals (:name, :title, :releasedIn)

· Multiple connected nodes

Below are beginner-friendly SPARQL examples, progressing from simple to more advanced.

1. Get All People

Equivalent SQL thinking:

SELECT * FROM Person

SPARQL:

PREFIX : <http://example.org/marvel/>

SELECT ?person
WHERE {
    ?person a :Person .
}