Entity–relationship diagram

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Example definition erd.dis: Tables with typed columns and relationships in crow's-foot notation.

It is explained in 17.3 Entity–relationship diagram — compartments from children, crow's-foot markers.

What it demonstrates

From 17.3 Entity–relationship diagram — compartments from children, crow's-foot markers:

This example shows notation driven by the model. Columns are child elements listed in a compartment, with conditional item styles and icons. Relationship markers are computed from the cardinality attributes (erZeroOrMany, erOne, …). The line is dashed for non-identifying relationships. Cardinality labels sit at both ends and only appear when zoomed in. Tables align to a 20 px grid while bendpoints use a 10 px grid. Ids are natural (derived from table and column names), persistence is YAML, and a plugin provides SQL export.

Views generated from the file

These views are drawn by this site from erd.dis itself: its metamodel, and the layers it fills. They are not the notation the definition draws; that appears in an IDE that runs it.

Generated from erd.dis at 4e69c28

Diagram as text (Mermaid)

classDiagram
  accTitle: Metamodel of the Entity–relationship diagram example
  accDescr: Class diagram of erd.dis: 2 node types (Table, Column) and 1 relation types (Relationship), with their typed attributes, inheritance, containment and relation ends.
  class Table {
    +string name
    +string schema
    +text comment
  }
  class Column {
    +string name
    +SqlType dataType
    +bool nullable
    +bool primaryKey
    +Column references
  }
  class Relationship {
    <<relation>>
    +string name
    +Cardinality sourceCardinality
    +Cardinality targetCardinality
    +bool identifying
  }
  Table "1" *-- "1..*" Column : contains
  Relationship --> Table : source
  Relationship --> Table : target

Generated from erd.dis at 4e69c28

Diagram as text (Mermaid)

flowchart LR
  accTitle: Layers of erd.dis
  accDescr: The eight DISL layers in order. erd.dis fills 8 of them: Metamodel (5 items), Coordinates (2 items), Notation (4 items), Toolbox (6 items), Constraints (3 items), Behavior (1 items), Layout (2 items), Persistence (6 items).
  L1["1 · Metamodel<br/>5 items"]
  L2["2 · Coordinate systems, placement and snapping<br/>2 items"]
  L3["3 · Notation (visual definition)<br/>4 items"]
  L4["4 · Toolbox, context tools and forms<br/>6 items"]
  L5["5 · Constraints<br/>3 items"]
  L6["6 · Behavior<br/>1 items"]
  L7["7 · Layout<br/>2 items"]
  L8["8 · Persistence<br/>6 items"]
  L1 --> L2 --> L3 --> L4 --> L5 --> L6 --> L7 --> L8
  classDef filled stroke-width:3px
  classDef empty stroke-dasharray:4 4
  class L1 filled
  class L2 filled
  class L3 filled
  class L4 filled
  class L5 filled
  class L6 filled
  class L7 filled
  class L8 filled

• Layer 1 — Metamodel: 5 items
• Layer 2 — Coordinate systems, placement and snapping: 2 items
• Layer 3 — Notation (visual definition): 4 items
• Layer 4 — Toolbox, context tools and forms: 6 items
• Layer 5 — Constraints: 3 items
• Layer 6 — Behavior: 1 items
• Layer 7 — Layout: 2 items
• Layer 8 — Persistence: 6 items

The file

Download erd.dis (9,674 bytes, unchanged from the source).

{
  "$schema": "https://etalii.net/adp/disl/schema/0.1/disl.schema.json#/$defs/Specification",
  "disl": "0.1",
  "language": {
    "id": "org.example.erd",
    "version": "2.0.0",
    "label": "Entity–relationship diagram",
    "doc": "Tables with typed columns and relationships in crow's-foot notation."
  },

  "metamodel": {
    "enums": {
      "SqlType": {
        "extensible": true,
        "values": { "uuid": {}, "text": {}, "varchar": {}, "int": {}, "bigint": {}, "numeric": {},
                    "bool": {}, "date": {}, "timestamptz": {}, "jsonb": {} }
      },
      "Cardinality": {
        "values": {
          "one": { "label": "Exactly one" },
          "zeroOrOne": { "label": "Zero or one" },
          "oneOrMany": { "label": "One or many" },
          "zeroOrMany": { "label": "Zero or many" }
        }
      }
    },
    "types": {
      "Table": {
        "attributes": {
          "name": { "type": "string", "required": true, "key": true, "pattern": "^[a-z_][a-z0-9_]*$", "unique": "diagram",
                    "doc": "snake_case table name." },
          "schema": { "type": "string", "default": "public" },
          "comment": { "type": "text" }
        },
        "children": { "allowed": ["Column"], "ordered": true, "min": 1,
                      "slots": { "columns": { "allowed": ["Column"], "min": 1 } } }
      },
      "Column": {
        "attributes": {
          "name": { "type": "string", "required": true, "key": true, "unique": "parent" },
          "dataType": { "type": "SqlType", "default": "text", "label": "Type" },
          "nullable": { "type": "bool", "default": true },
          "primaryKey": { "type": "bool", "default": false, "label": "Primary key" },
          "references": { "type": "Column", "doc": "Foreign-key target column." }
        }
      }
    },
    "relations": {
      "Relationship": {
        "source": "Table",
        "target": "Table",
        "directed": false,
        "allowSelfLoops": true,
        "attributes": {
          "name": { "type": "string" },
          "sourceCardinality": { "type": "Cardinality", "default": "one" },
          "targetCardinality": { "type": "Cardinality", "default": "zeroOrMany" },
          "identifying": { "type": "bool", "default": false,
                           "doc": "Identifying relationships make the parent key part of the child key." }
        }
      }
    }
  },

  "coordinates": {
    "snapProfiles": {
      "coarse": { "both": { "grid": { "spacing": 20 } }, "targets": ["objects", "rule"],
                  "doc": "Tables align to a 20 px grid; edges snap their bendpoints to 10 px.",
                  "bendpoints": { "both": { "grid": { "spacing": 10 } } } }
    },
    "systems": {
      "canvas": { "kind": "cartesian", "x": { "kind": "linear" }, "y": { "kind": "linear" }, "snapping": "coarse",
                  "grid": { "visible": true, "style": "lines", "spacing": 20, "majorEvery": 5 } }
    }
  },

  "notation": {
    "styles": {
      "table": { "fill": "#FFFFFF", "stroke": { "color": "#444441", "width": 1 }, "cornerRadius": 6,
                 "font": { "family": "Inter, sans-serif", "size": 12 }, "shadow": { "dx": 0, "dy": 1, "blur": 3, "color": "#00000022" } }
    },
    "nodes": {
      "Table": {
        "shape": { "type": "roundedRect", "params": { "radius": 6 } },
        "style": "table",
        "size": { "default": [220, 120], "autoSize": "fitHeight", "resizable": "horizontal" },
        "labels": [
          { "id": "name", "text": { "attribute": "name" }, "position": "top", "editable": "inline",
            "background": { "fill": "#EEEDFE", "padding": [6, 8] },
            "style": { "font": { "weight": 600, "color": "#3C3489" } } }
        ],
        "compartments": [
          { "id": "columns",
            "items": { "children": ["Column"], "slot": "columns" },
            "itemText": { "cel": "item.name + '  ' + item.dataType + (item.nullable ? '' : ' not null')" },
            "itemIcon": { "cel": "item.primaryKey ? 'key' : (has(item.references) ? 'link' : '')" },
            "itemConditions": [ { "when": "item.primaryKey", "style": { "font": { "weight": 600, "decoration": "underline" } } } ],
            "separator": { "color": "#D3D1C7", "width": 0.5 },
            "overflow": "ellipsis", "maxItems": 20,
            "editable": { "add": true, "remove": true, "reorder": true, "inline": true },
            "emptyText": "No columns" }
        ],
        "anchors": { "mode": "sides", "spread": true },
        "form": { "form": "columnsTable", "interaction": "onDoubleClick", "minZoom": 0.8, "fallback": "labels" },
        "lod": [ { "maxZoom": 0.4, "hide": ["compartments"] } ]
      },
      "Column": { "shape": "none", "labels": [] }
    },
    "edges": {
      "Relationship": {
        "line": {
          "stroke": { "color": "#444441", "width": 1.25,
                      "dash": { "cel": "self.identifying ? 'solid' : 'dashed'" } },
          "routing": "orthogonal",
          "cornerRadius": 0,
          "avoidNodes": true,
          "minSegmentLength": 18,
          "startDirection": "normal",
          "endDirection": "normal",
          "bendpoints": { "editable": true }
        },
        "jumps": { "style": "gap", "size": 5 },
        "sourceMarker": { "cel": "'er' + self.sourceCardinality.substring(0, 1).upperAscii() + self.sourceCardinality.substring(1)" },
        "targetMarker": { "cel": "'er' + self.targetCardinality.substring(0, 1).upperAscii() + self.targetCardinality.substring(1)" },
        "labels": [
          { "id": "name", "text": { "attribute": "name" }, "at": "middle", "side": "above", "orientation": "upright",
            "style": { "font": { "style": "italic", "size": 11 } }, "editable": "inline" },
          { "id": "srcCard", "text": { "cel": "enumLabel('Cardinality', self.sourceCardinality)" }, "at": "start", "offset": 20,
            "side": "below", "style": { "font": { "size": 10, "color": "#888780" } }, "visible": { "cel": "env.zoom > 1.2" } },
          { "id": "tgtCard", "text": { "cel": "enumLabel('Cardinality', self.targetCardinality)" }, "at": "end", "offset": 20,
            "side": "below", "style": { "font": { "size": 10, "color": "#888780" } }, "visible": { "cel": "env.zoom > 1.2" } }
        ]
      }
    }
  },

  "forms": {
    "columnsTable": {
      "for": "Table",
      "usage": ["embedded", "inspector"],
      "layout": { "density": "compact" },
      "items": [
        { "attribute": "name" },
        { "kind": "field", "attribute": "comment", "widget": "textarea", "rows": 2 }
      ]
    }
  },

  "toolbox": {
    "groups": [
      { "id": "model", "label": "Model", "tools": [
        { "id": "table", "creates": "Table", "shortcut": "T" },
        { "id": "rel", "creates": "Relationship", "shortcut": "R" },
        { "id": "rel1n", "creates": "Relationship", "variantOf": "rel", "label": "One-to-many",
          "initial": { "sourceCardinality": "one", "targetCardinality": "zeroOrMany" } },
        { "id": "rel11", "creates": "Relationship", "variantOf": "rel", "label": "One-to-one",
          "initial": { "sourceCardinality": "one", "targetCardinality": "zeroOrOne" } }
      ] }
    ],
    "contextTools": [
      { "for": ["Table"], "tools": [
        { "kind": "create-child", "creates": "Column", "slot": "columns", "label": "Add column", "icon": "plus", "position": "bottom" }
      ] }
    ]
  },

  "constraints": {
    "rules": [
      { "id": "hasPrimaryKey", "scope": "Table",
        "rule": "self.children.exists(c, c.primaryKey)",
        "severity": "warning", "message": { "cel": "'Table ' + self.name + ' has no primary key.'" },
        "fixes": [ { "label": "Add an id column",
                     "actions": [ { "create": { "type": "'Column'", "parent": "self", "slot": "'columns'",
                                                "attributes": { "name": "'id'", "dataType": "'uuid'", "primaryKey": "true", "nullable": "false" } } } ] } ] },
      { "id": "fkTypeMatches", "scope": "Column", "when": "has(self.references)",
        "rule": "self.references.dataType == self.dataType",
        "attribute": "dataType",
        "message": { "cel": "'Foreign key type ' + self.dataType + ' does not match ' + self.references.parent.name + '.' + self.references.name + ' (' + self.references.dataType + ').'" },
        "fixes": [ { "label": "Use the referenced column's type", "actions": [ { "set": { "dataType": "self.references.dataType" } } ] } ] },
      { "id": "pkNotNull", "scope": "Column", "when": "self.primaryKey", "rule": "!self.nullable",
        "enforcement": "prevent-and-report", "attribute": "nullable",
        "message": "Primary key columns cannot be nullable." }
    ]
  },

  "behavior": {
    "hooks": [
      { "id": "pkImpliesNotNull", "on": "change", "for": "Column", "attribute": "primaryKey", "phase": "before",
        "when": "self.primaryKey", "actions": [ { "set": { "nullable": "false" } } ] }
    ]
  },

  "layout": {
    "algorithms": { "orthogonal": { "algorithm": "elk:org.eclipse.elk.layered", "direction": "right",
                                    "edgeRouting": "orthogonal", "spacing": { "node": 60, "layer": 120 } } },
    "default": "orthogonal"
  },

  "persistence": {
    "format": "yaml",
    "ids": { "strategy": "natural", "stable": true },
    "ordering": { "elements": "tree" },
    "view": { "store": ["bounds", "waypoints", "labelOffsets", "collapsed"] },
    "export": [ { "format": "plugin:sql-ddl", "label": "SQL DDL" } ]
  },

  "plugins": {
    "sql-ddl": { "version": "^1.0.0", "provides": ["export"], "required": false,
                 "doc": "Generates CREATE TABLE statements." }
  }
}

In an IDE

No IDE host runs this example yet.

Source

Specification

DISL 0.5, Draft, 2026-10-19

Repository

etalii-adp/etalii.adp

Revision

4e69c28 of specifications/disl/DISL-specification.md

Generated

2026-11-03, by this site from that revision, unchanged

Licence

Apache-2.0, Copyright © Peter Vrenken 2026

Found an error? Report a problem to etalii-adp/etalii.adp, where the specification is written.