Below is an overview of EdgeDB’s terminology. Use it as a roadmap, but don’t worry if it doesn’t all make sense immediately. The following pages go into detail on each concept below.
An EdgeDB instance is a collection of databases that store their data in a shared directory and are managed by a running EdgeDB process. You can create, start, stop, and destroy instances on your local computer with the EdgeDB CLI. Instances listen for incoming queries on a connection port.
Each instance can contain several databases, each with a unique name. At
the time of creation, all instances contain a single database called
edgedb. This is the default database; all incoming queries are executed
against it unless otherwise specified.
Each database can contain several modules, each with a unique name. Modules
can be used to organize large schemas into logical units. In SDL, module
blocks are used to declare types inside a particular module.
module default {
# declare types here
}
module another_module {
# more types here
}Some module names (std, math, cal, schema, sys, cfg)
are reserved by EdgeDB and contain pre-defined types, utility functions, and
operators. It’s common to declare an application’s entire schema inside a
single module called default.
Schemas are predominantly composed of object types, the EdgeDB equivalent
of SQL tables. Object types contain properties and links. Both
properties and links are associated with a unique name (e.g.
first_name, friends, etc) and a cardinality, which can be either
single (the default) or multi. Object types can be augmented with
constraints, annotations, and indexes.
Properties correspond to either a scalar type (e.g. str, int64) or
a collection type (an array or a tuple). They can be augmented with
constraints, annotations, and default values. They can also be
marked as readonly.
Links represent relationships between object types. Like properties, they can marked as readonly and augmented with constraints, annotations, and default values. They can optionally contain link properties.
Links and properties can also be computed. Computed links and properties are not physically stored in the database, but they can be used in queries just like non-computed ones. The value will be computed as needed.
You can also declare custom strongly-typed functions in addition to the large library of built-in functions and operators.
