About ERdoc

ERdoc is a markup language for creating Entity-Relationship models through text (ER documents). The Playground is a web-based tool to visualize ER documents as ER diagrams using common notations.

The ERdoc language features the core concepts of the ER model (entities, relationships, attributes) and other advanced features such as aggregations, subclass/superclass, n-ary relationships, cardinality and participation constraints.

Examples

An ER document is composed of a sequence of entity, relationship or aggregation declarations. The following example features ternary relationships, weak entities, inheritance and other concepts of the ER model:

entity Employee {
    e_id key
    name
}
 
entity Department {
    d_number key
    d_name
}
 
relation Manages(Department: [Management N!, Research 1])
 
 
relation Works_for(Employee 1, Department N!)
 
entity Project {
    p_id key
    p_name
}
 
relation Controls(Department, Project 1!)
 
relation Works_on(Employee M, Project N) {
    hours
}
 
entity Part {
    p_number key
    p_name
}
 
entity Screw extends Part {
    head_style
}
 
entity Supplier {
    s_id key
    s_name
}
 
relation Supplies(Project M, Part N!, Supplier P!) {
    Quantity
}
 
entity Dependent depends on Dependent_of {
    Dep_name pkey
    Gender
}
 
relation Dependent_of(Employee, Dependent 1!)

In the playground, this example will generate the following ER diagram (after adjusting some positions), here we are using (min, max) notation.

Once you get familiar with the syntax, you'll find it much faster to create ER diagrams this way rather than using conventional, visual charting tools.

The following ER document declares two entities and a relationship between them:

entity Student {
  id key
  name
  age
}
 
entity University {
  name 
  address: [city, street, number]
  university_id key
}
 
relation Studies_at(Student 1, University N!) {
  enrollment_date
}

And the ER diagram (using Arrow notation):

Read the next sections to learn more about ERdoc's syntax.