This document describes the serialization format for LionWeb version 2024.1 chunks.

Conventions used in this document

  • italic words refer to concepts defined by JSON.

  • bold words refer to concepts defined in this document.

  • monospaced words describe verbatim contents of the serialization.

  • ALL-CAPS key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 (RFC2119, RFC8174) when, and only when, they appear in all capitals, as shown here.

  • "processed document" refers to the character sequence that’s parsed or written, e.g. a file or network stream.

  • Footnotes refer to more discussions and rationale, but are non-normative.

Design goals

We want to provide boring and proven infrastructure, so that innovation can be built on top of it. We do not take any measures to reduce the amount of transmitted data.[1] We strive for shallow structures to enable stream-based processing.

Description

LionWeb node serialization format is defined in JSON (RFC 8259).

We follow the advice of RFC 8259 to be "interoperable", i.e. we assume object keys are unique, and their order is undefined. Any violations SHOULD be reported as error.[2]

Overview of structures

No unspecified members are allowed anywhere in the structure.[3]

Diagram

Root structure

Root level MUST be an object with three members, called serialization chunk.

The first member SHOULD be key serializationFormatVersion with a string value.[4][2][5] The value MUST be a non-empty string (without leading or trailing whitespace)[6] describing the serialization format version used to create the processed document, according to Versions.

The second member SHOULD be key languages with an array value.[7][8][2] Each element in the value array MUST adhere to Language structure. The order of elements is undefined. elements MUST contain all language/version referred to by any Meta-pointer in the processed document. Each element MUST be unique with respect to all its members.

The third member SHOULD be key nodes with an array value.[9][2] Each element in the value array MUST adhere to Node structure. The order of elements is undefined. Each element MUST be unique with respect to the value of its key id.

Language structure

Each used language MUST be an object.[10] The order of members is undefined.

Note
 If the chunk describes a language (M2), it might include instances of builtins' language entities. In this case, builtins MUST be listed as used language like any other language.[11]

The object MUST contain the following members:[7]

Language key

A string according to Key spec. Refers to the key of the language.

Language version

A string with any contents[12][13], MUST NOT be empty.[14] Refers to the version of the language.

Meta-pointer

A meta-pointer is a reference from M1 to M2.[15][16] It’s used at several places within Node structure.

Each meta-pointer MUST be an object. The order of members is undefined.

The object MUST contain the following members:

Node structure

Each node MUST be an object.[17] The order of members is undefined.

The object MUST contain the following members:[18][19][20]

  • key id with string value, adhering to Id value.

  • key classifier[21][22] with object value, adhering to Meta-pointer. The meta-pointer's key's value refers to the key of the Concept or Annotation this node is an instance of.

  • key properties with array value, each element adhering to Property. The order of elements is undefined.[23]

  • key containments[24][25] with array value, each element adhering to Containment. The order of elements is undefined.[23]

  • key references[26] with array value, each element adhering to Reference. The order of elements is undefined.[23]

  • key annotations[27] with array value, each element adhering to Annotation. The order of elements MUST be maintained.[28]

  • key parent[29] with string or null value, adhering to Parent.

For all features (i.e. properties, containments, and references) defined for a node's classifier:[9]

  • During serialization, we SHOULD include every feature, even if unset. In the latter case:

    • the property MUST have value = null;

    • the containment MUST have children = empty array;

    • the reference MUST have targets = empty array;

  • During deserialization, we MUST accept a node even if not all defined features are present.

  • We MAY accept undefined features during deserialization if we can deal with them in a meaningful manner.

Note
 We currently cannot store "invalid text" (i.e. user-entered text that does not adhere to the underlying structure and/or constraints) in the model. We will support this in a future release.[30]

Id value

A string according to Identifier spec. Defines the id of this node.

Property

Each property MUST be an object. The order of members is undefined.

The object MUST contain the following members:

  • key property with object value, adhering to Meta-pointer. The meta-pointer's key's value refers to the key of the Property this property is an instance of.

  • key value with value as one of

    • string[31] containing the value of the property referenced by the property. Refer to Property serialization for the specification of the value format. Can be an empty string.

    • null to explicitly specify the property to be unset.

Containment

Each containment MUST be an object. The order of members is undefined.

The object MUST contain the following members:

  • key containment with object value, adhering to Meta-pointer. The meta-pointer's key's value refers to the key of the Containment this containment is an instance of.

  • key children with array value with string elements. Each element adheres to Identifier spec, and refers to the id of the contained node. The order of elements MUST be maintained.[28]

    Note
    		 Each children element is the inverse relation of a parent.
    Note
    		 The children node can be contained in the processed document, but also can be outside the processed document (i.e. not contained in the processed document).

Reference

Each reference MUST be an object. The order of members is undefined.

The object MUST contain the following members:

  • key reference with object value, adhering to Meta-pointer. The meta-pointer's key's value refers to the key of the Reference this reference is an instance of.

  • key targets with array value with _object elements. The order of elements MUST be maintained.[28] Each element MUST have the following members in undefined order:[26]

    • key resolveInfo[32] with value as one of:

      • string containing resolveInfo, a textual hint that might be used to find the target node of this reference. Interface INamed SHOULD be used as a default, if available. The exact value depends on the implementation. Can be an empty string.

      • null if no resolveInfo is available.

    • key reference[33] with value as one of:

      • string according to Identifier spec. Refers to the id of the target node.

        Note
        		 The referred node can be contained in the processed document, but also can be outside the processed document (i.e. not contained in the processed document).

      • null if the id of the target node is not known.

Annotation

Each annotation MUST be a string. It adheres to Identifier spec, and refers to the id of the contained annotation node.

Note
 Each annotation element is the inverse relation of a parent.[27]
Note
 The annotation node can be contained in the processed document, but also can be outside the processed document (i.e. not contained in the processed document).

Parent

One of

  • string according to Identifier spec. Refers to the id of the node containing this node.

    Note
    		 parent is the inverse relation of either one containment or one annotation.[34]
    Note
    		 The referred node can be contained in the processed document, but also can be outside the processed document (i.e. not contained in the processed document).

  • null if

    • This node is a root node, i.e. this node does not have a parent.

    • This serialization is sent as an update request.

Property serialization

All property values MUST be serialized as JSON string.[31][35]. An unset property SHOULD be serialized as JSON null.

String

LionCore Strings might be any string, of any length, including (but not limited to):

  • empty string: ""

  • only containing whitespace: " "

  • containing escaped characters as per JSON spec: "They said:\n \"Hello!\""

  • containing extended Unicode characters: "😐"

  • containing escaped Unicode characters: "\uD83D\uDE10"

Boolean

LionCore Booleans MUST be encoded as exactly one of these JSON strings:

  • "true"

  • "false"

Booleans MUST NOT be encoded with leading or trailing whitespace, uppercase characters, short forms (like t or f), or decimal representation (like 1, 0, -1).

Integer

LionCore Integers MUST be encoded as JSON string.

  • Integers MUST be represented in base-10.

  • The digits can be prefixed with either + (plus) or - (minus).[36]

  • Integers MUST NOT be prefixed by leading zeros.

  • Integers can contain value zero with any prefix, i.e. 0, -0, or +0.

  • Integers MUST NOT contain leading or trailing whitespace.

  • LionWeb does NOT limit the range of the integer value.[37] An implementation MAY refuse a model containing an integer value outside the supported range.

Examples of valid Integer encodings

  • "0"

  • "+0"

  • "-0"

  • "123"

  • "-100000"

  • "+999"

  • "100000000200000000300000000400000000500000000600000000700000000800000000900000000999999999"

  • "-999999999900000000800000000700000000600000000500000000400000000300000000200000000100000000"

Examples of invalid Integer encodings

  • ""

  • 123

  • -1

  • "+-0"

  • "++1"

  • "00002"

  • "0xAA12"

  • " 5"

  • "-6 "

Structured Datatype

LionCore StructuredDataType MUST be encoded as JSON string. The string contains a JSON object according to spec (RFC 8259) with proper escaping: all double quotes, line breaks, etc. MUST be escaped to form a proper JSON string.

The contents of the string are formed as follows: A LionCore StructuredDataType is encoded as JSON object. Each Field forms one member, with the field’s key as JSON key and the field’s value as JSON value. For fields of type String, Boolean, Integer, and Enumeration literal, the value is encoded as JSON string in the same way as for a property. For fields of type Structured Datatype, the value is encoded as JSON object if the field is set, otherwise as JSON null.

Structured datatypes used in the examples
Note
 The format used in this example is non-normative. 
enumeration Currency                   [id aa, key currency]
  literal EUR                          [id a0, key cur-eur]
  literal GBP                          [id a1, key cur-gbp]

structured datatype Amount             [id 10, key amount]
  value: Integer                       [id 11, key amount-val]
  currency: Currency                   [id 12, key amount-cur]
  digital: Boolean                     [id 13, key digital]

structured datatype Decimal            [id 20, key decimal]
  int: Integer                         [id 21, key decimal-int]
  frac: Integer                        [id 22, key decimal-frac]

structured datatype ComplexNumber      [id 30, key complex]
  real: Decimal                        [id 31, key complex-real]
  imaginary: Decimal                   [id 32, key complex-imaginary]

structured datatype FullyQualifiedName [id 50, key fqn]
  name: String                         [id 40, key nm]
  nested: FullyQualifiedName           [id 55, key nested]
Valid examples

  • Amount 42 EUR non-digital: "{\n \"amount-val\": \"42\",\n \"amount-cur\": \"cur-eur\",\n \"digital\": \"false\"\n}"

    unescaped content:

    {
  "amount-val":  "42",
  "amount-cur": "cur-eur",
  "digital": "false"
}

  • Decimal 42.0: "{\"decimal-int\": \"42\", \"decimal-frac\": \"0\"}"

    unescaped content:

    {"decimal-int": "42", "decimal-frac": "0"}

  • ComplexNumber 23.17 + 42.0i: "{\n\"complex-real\": { \"decimal-int\": \"23\", \"decimal-frac\": \"17\"},\n\"complex-imaginary\": { \"decimal-int\": \"42\", \"decimal-frac\": \"0\"}\n}"

    unescaped content:

    {
"complex-real": { "decimal-int": "23", "decimal-frac": "17"},
"complex-imaginary": { "decimal-int": "42", "decimal-frac": "0"}
}

  • FullyQualifiedName com.example.subdomain: "{\n \"nm\": \"com\",\n \"nested\": {\n \"nm\": \"example\",\n \"nested\": {\n \"nm\": \"subdomain\",\n \"nested\": null\n }\n }\n}"

    unescaped content:

    {
  "nm": "com",
  "nested": {
    "nm": "example",
    "nested": {
      "nm": "subdomain",
      "nested": null
    }
  }
}
Invalid examples

  • Amount with non-string field values: "{\n \"amount-val\": 42,\n \"amount-cur\": \"cur-eur\",\n \"digital\": false\n}"

    unescaped content:

    {
  "amount-val":  42,
  "amount-cur": "cur-eur",
  "digital": false
}

  • Decimal with missing field: "{\"decimal-int\": \"42\"}"

    unescaped content:

    {"decimal-int": "42"}

  • Decimal with null value for field with primitive type: "{\"decimal-int\": \"42\", \"decimal-frac\": null}"

    unescaped content:

    {"decimal-int": "42", "decimal-frac": null}

  • Decimal with missing outer braces: "\"decimal-int\": \"42\", \"decimal-frac\": \"0\""

    unescaped content:

    "decimal-int": "42", "decimal-frac": "0"

  • Decimal with field name as JSON keys: "{\"int\": \"42\", \"frac\": \"0\"}"

    unescaped content:

    {"int": "42", "frac": "0"}

  • Decimal with invalid field value: "{\"decimal-int\": \"42\", \"decimal-frac\": \"nothing\"}"

    unescaped content:

    {"decimal-int": "42", "decimal-frac": "nothing"}

  • Decimal with unknown field: "{\"decimal-int\": \"42\", \"decimal-frac\": \"0\", \"decimal-comment\": \"life question?\"}"

    unescaped content:

    {"decimal-int": "42", "decimal-frac": "0", "decimal-comment": "life question?"}

  • ComplexNumber with recursively nested structured datatype: "{\n\"complex-real\": \"{ \\\"decimal-int\\\": \\\"23\\\", \\\"decimal-frac\\\": \\\"17\\\"}\",\n\"complex-imaginary\": { \"decimal-int\": \"42\", \"decimal-frac\": \"0\"}\n}"

    unescaped content:

    {
"complex-real": "{ \"decimal-int\": \"23\", \"decimal-frac\": \"17\"}",
"complex-imaginary": { "decimal-int": "42", "decimal-frac": "0"}
}

  • FullyQualifiedName with null as string value for unset nested structured datatype: "{\n \"nm\": \"com\",\n \"nested\": {\n \"nm\": \"example\",\n \"nested\": {\n \"nm\": \"subdomain\",\n \"nested\": \"null\"\n }\n }\n}"

    unescaped content:

    {
  "nm": "com",
  "nested": {
    "nm": "example",
    "nested": {
      "nm": "subdomain",
      "nested": "null"
    }
  }
}

Enumeration literal

LionCore Enumeration literals MUST be encoded as JSON string value according to Key spec. MUST refer to the key of an EnumerationLiteral of the Enumeration defined as type of this Property.[12]

Examples

Minimal

{
  "serializationFormatVersion": "2024.1",
  "languages": [],
  "nodes": []
}

Minimal node

{
  "serializationFormatVersion": "2024.1",
  "languages": [
    {
      "key": "myLanguage",
      "version": "2"
    }
  ],
  "nodes": [
    {
      "id": "aaa",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "myConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    }
  ]
}

Property variants

For this example, we need to define an enumeration and a concept that uses the enumeration.

Note
 The format used in this example is non-normative.

Assume this enumeration:

enumeration DaysOfWeek [id 23, key days-of-week]

  literal Monday       [id 34, key monday]
  literal Tuesday      [id 2,  key tttt]
  literal Wednesday    [id 55, key 12398712]

And this concept:

concept OpeningTime           [id 44, key time_to_open]
  property day: DaysOfWeek    [id 42, key day]
  property startHour: Integer [id 22, key starthour]
  property endHour: Integer   [id 89, key endhour]
{
  "serializationFormatVersion": "2024.1",
  "languages": [
    {
      "key": "myLanguage",
      "version": "2"
    }
  ],
  "nodes": [
    {
      "id": "bbb",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "myConceptId"
      },
      "properties": [
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "stringPropertyId"
          },
          "value": "my string value"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "integerPropertyId"
          },
          "value": "123"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "booleanPropertyId"
          },
          "value": "true"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "structuredDatatypeId"
          },
          "value": "{ \"name\": \"Bob\" }"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "unsetPropertyId"
          },
          "value": null
        }
      ],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    },
    {
      "id": "21",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "time_to_open"
      },
      "properties": [
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "day"
          },
          "value": "tttt"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "starthour"
          },
          "value": "9"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "endhour"
          },
          "value": "5"
        }
      ],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    }
  ]
}

Containment variants

{
  "serializationFormatVersion": "2024.1",
  "languages": [
    {
      "key": "myLanguage",
      "version": "2"
    }
  ],
  "nodes": [
    {
      "id": "ccc",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "myConceptId"
      },
      "properties": [],
      "containments": [
        {
          "containment": {
            "language": "myLanguage",
            "version": "2",
            "key": "emptyContainmentId"
          },
          "children": []
        },
        {
          "containment": {
            "language": "myLanguage",
            "version": "2",
            "key": "singleContainmentId"
          },
          "children": [
            "cdd"
          ]
        },
        {
          "containment": {
            "language": "myLanguage",
            "version": "2",
            "key": "multiContainmentId"
          },
          "children": [
            "cee",
            "cff",
            "cgg"
          ]
        }
      ],
      "references": [],
      "annotations": [],
      "parent": null
    },
    {
      "id": "cgg",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "differentConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    },
    {
      "id": "cdd",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "otherConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "ccc"
    },
    {
      "id": "cee",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "differentConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    }
  ]
}

node with id cff is outside the processed document.

Reference variants

We support different kinds of targets.[38]

{
  "serializationFormatVersion": "2024.1",
  "languages": [
    {
      "key": "myLanguage",
      "version": "2"
    }
  ],
  "nodes": [
    {
      "id": "ddd",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "myConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "emptyReferenceId"
          },
          "targets": []
        },
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "singleReferenceId"
          },
          "targets": [
            {
              "resolveInfo": "some name",
              "reference": "dee"
            }
          ]
        },
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "multiReferenceId"
          },
          "targets": [
            {
              "resolveInfo": "self-reference",
              "reference": "ddd"
            },
            {
              "resolveInfo": "only resolve info",
              "reference": null
            }
          ]
        },
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "noResolveInfoReferenceId"
          },
          "targets": [
            {
              "resolveInfo": null,
              "reference": "dee"
            }
          ]
        },
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "neitherResolveInfoNorReferenceId"
          },
          "targets": [
            {
              "resolveInfo": null,
              "reference": null
            }
          ]
        }
      ],
      "annotations": [],
      "parent": null
    },
    {
      "id": "dee",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "differentConceptId"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    }
  ]
}

Annotation variants

For this example, we need to define some annotations and their annotated concepts.

Note
 The format used in this example is non-normative.

Assume these annotations:

annotation Docu [id 23, key docuAnn]
  multiple = true
  annotates = IDocumentable
  property docu: String [id 34, key Docu-docu]

annotation ExtendedDocu extends Docu [id 20, key docuExtended]
  property moreDocu: String [id mds, key MDS]

annotation Marker [id 22, key myMarker]
  multiple = false
  annotates = Node

annotation TrashCan [id 99, key throwAway]
  multiple = false
  annotates = Node
  containment trash: 0..* Node  [id 2, key tat]

interface JavaInfo [id 33, key jv]
  property javaVersion: String  [id 33a, key jvA]

annotation MappedToClass implements JavaInfo [id mtc, key MTC]
  multiple = false
  annotates = Classifier
  reference javaClass: 1 BaseLanguageClass [id jjj, key JJJ]


annotation UsesMapping implements JavaInfo [id um, key UM]
  multiple = false
  annotates = Feature
  reference mapping: 1 MappedToClass [id jjj1, key JJJ1]

And these concepts:

interface IDocumentable [id 50, key 51]

concept BaseLanguageClass implements IDocumentable [id 60, key 61]

concept OtherLanguageConcept [id 70, key otherLangConc]
  reference usesTrashCan: 0..1 TrashCan [id 72, key usesTrashCan]
{
  "serializationFormatVersion": "2024.1",
  "languages": [
    {
      "key": "myLanguage",
      "version": "2"
    },
    {
      "key": "BaseLanguage",
      "version": "1"
    },
    {
      "key": "LionWeb-M3",
      "version": "2024.1"
    }
  ],
  "nodes": [
    {
      "id": "ccc",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "61"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [
        "marker",
        "docu1",
        "docu2",
        "localTrash"
      ],
      "parent": null
    },
    {
      "id": "marker",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "myMarker"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "61"
    },
    {
      "id": "docu1",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "docuAnn"
      },
      "properties": [
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "Docu-docu"
          },
          "value": "This is a very important BaseLanguageClass"
        }
      ],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "61"
    },
    {
      "id": "docu2",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "docuExtended"
      },
      "properties": [
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "Docu-docu"
          },
          "value": "We want to say a few more things about this BaseLanguageClass"
        },
        {
          "property": {
            "language": "myLanguage",
            "version": "2",
            "key": "MDS"
          },
          "value": "Here be dragons"
        }
      ],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "61"
    },
    {
      "id": "localTrash",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "throwAway"
      },
      "properties": [],
      "containments": [
        {
          "containment": {
            "language": "myLanguage",
            "version": "2",
            "key": "tat"
          },
          "children": [
            "old1",
            "old2"
          ]
        }
      ],
      "references": [],
      "annotations": [],
      "parent": "61"
    },
    {
      "id": "old1",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "SomeConcept"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "localTrash"
    },
    {
      "id": "old2",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "YetAnotherConcept"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": "localTrash"
    },
    {
      "id": "bbb",
      "classifier": {
        "language": "LionWeb-M3",
        "version": "2024.1",
        "key": "Concept"
      },
      "properties": [],
      "containments": [
        {
          "containment": {
            "language": "LionWeb-M3",
            "version": "2024.1",
            "key": "Classifier-features"
          },
          "children": [
            "bbb-prop"
          ]
        }
      ],
      "references": [],
      "annotations": [
        "javaMapping"
      ],
      "parent": null
    },
    {
      "id": "bbb-prop",
      "classifier": {
        "language": "LionWeb-M3",
        "version": "2024.1",
        "key": "Property"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [
        "typeUseMapping"
      ],
      "parent": "bbb"
    },
    {
      "id": "javaMapping",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "MTC"
      },
      "properties": [],
      "containments": [],
      "references": [
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "JJJ"
          },
          "targets": [
            {
              "resolveInfo": null,
              "reference": "javaClass"
            }
          ]
        }
      ],
      "annotations": [],
      "parent": "bbb"
    },
    {
      "id": "typeUseMapping",
      "classifier": {
        "language": "myLanguage",
        "version": "2",
        "key": "UM"
      },
      "properties": [],
      "containments": [],
      "references": [
        {
          "reference": {
            "language": "myLanguage",
            "version": "2",
            "key": "JJJ1"
          },
          "targets": [
            {
              "resolveInfo": null,
              "reference": "javaMapping"
            }
          ]
        }
      ],
      "annotations": [],
      "parent": "bbb-prop"
    },
    {
      "id": "javaClass",
      "classifier": {
        "language": "BaseLanguage",
        "version": "1",
        "key": "ClassConcept"
      },
      "properties": [],
      "containments": [],
      "references": [],
      "annotations": [],
      "parent": null
    }
  ]
}

Versions

Note
 The term "version" is a bit ambiguous within LionWeb.[5] This section lists all versions as they appear in serializationFormatVersion and Language.version for languages LionWeb-M3 and LionWeb-builtins.

2024.1

Technical name: 2024.1

Refer to roadmap for details.

2023.1

Technical name: 2023.1

Initial version. Refer to roadmap for details.

JSON Schema for serialization

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://lionweb.io/serialization.schema.json",
  "title": "LionWeb Serialization",
  "type": "object",
  "properties": {
    "serializationFormatVersion": {
      "type": "string",
      "pattern": "^\\S+(.*\\S)?$"
    },
    "languages": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "key": {
            "$ref": "#/$defs/key"
          },
          "version": {
            "$ref": "#/$defs/version"
          }
        },
        "required": [
          "key",
          "version"
        ],
        "additionalProperties": false,
        "minProperties": 2,
        "maxProperties": 2
      },
      "uniqueItems": true
    },
    "nodes": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "id": {
            "$ref": "#/$defs/id"
          },
          "classifier": {
            "$ref": "#/$defs/metaPointer"
          },
          "properties": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "property": {
                  "$ref": "#/$defs/metaPointer"
                },
                "value": {
                  "oneOf": [
                    {
                      "type": "string"
                    },
                    {
                      "type": "null"
                    }
                  ]
                }
              },
              "required": [
                "property",
                "value"
              ],
              "additionalProperties": false,
              "minProperties": 2,
              "maxProperties": 2
            }
          },
          "containments": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "containment": {
                  "$ref": "#/$defs/metaPointer"
                },
                "children": {
                  "type": "array",
                  "items": {
                    "$ref": "#/$defs/id"
                  },
                  "uniqueItems": true
                }
              },
              "required": [
                "containment",
                "children"
              ],
              "additionalProperties": false,
              "minProperties": 2,
              "maxProperties": 2
            }
          },
          "references": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "reference": {
                  "$ref": "#/$defs/metaPointer"
                },
                "targets": {
                  "type": "array",
                  "items": {
                    "type": "object",
                    "properties": {
                      "resolveInfo": {
                        "oneOf": [
                          {
                            "type": "string"
                          },
                          {
                            "type": "null"
                          }
                        ]
                      },
                      "reference": {
                        "oneOf": [
                          {
                            "$ref": "#/$defs/id"
                          },
                          {
                            "type": "null"
                          }
                        ]
                      }
                    },
                    "required": [
                      "resolveInfo",
                      "reference"
                    ],
                    "additionalProperties": false,
                    "minProperties": 2,
                    "maxProperties": 2
                  }
                }
              },
              "required": [
                "reference",
                "targets"
              ],
              "additionalProperties": false,
              "minProperties": 2,
              "maxProperties": 2
            }
          },
          "annotations": {
            "type": "array",
            "items": {
              "$ref": "#/$defs/id"
            },
            "uniqueItems": true
          },
          "parent": {
            "oneOf": [
              {
                "$ref": "#/$defs/id"
              },
              {
                "type": "null"
              }
            ]
          }
        },
        "required": [
          "id",
          "classifier",
          "properties",
          "containments",
          "references",
          "annotations",
          "parent"
        ],
        "additionalProperties": false,
        "minProperties": 7,
        "maxProperties": 7
      },
      "uniqueItems": true
    }
  },
  "required": [
    "serializationFormatVersion",
    "languages",
    "nodes"
  ],
  "additionalProperties": false,
  "minProperties": 3,
  "maxProperties": 3,
  "$defs": {
    "id": {
      "type": "string",
      "minLength": 1,
      "pattern": "^[a-zA-Z0-9_-]+$"
    },
    "key": {
      "$ref": "#/$defs/id"
    },
    "version": {
      "type": "string",
      "minLength": 1
    },
    "metaPointer": {
      "type": "object",
      "properties": {
        "language": {
          "$ref": "#/$defs/key"
        },
        "version": {
          "$ref": "#/$defs/version"
        },
        "key": {
          "$ref": "#/$defs/key"
        }
      },
      "required": [
        "language",
        "version",
        "key"
      ],
      "additionalProperties": false,
      "minProperties": 3,
      "maxProperties": 3
    }
  }
}

Possible values for properties, containments, and references

Only bold entries are valid.[19]

1 A
Contents		 B
properties: {_ _ _}		 C
containments: {_ _ _}		 D
references: {_ _ _}

2 "a": "b"

property with id a has value b

containments value must be array

references value must be array

3 "c": ""

property with id c has value (empty string)

4 "d": " "

property with id d has value ` `(one space)

5 "e": null

property with id e has no value

6 (key f not present)

property with id f has no value

containment with id f does not contain any nodes

reference with id f does not point to any nodes

7 "g": []

properties value must be string

containment with id g does not contain any nodes

reference with id g does not point to any nodes

8 "h": [ "i" ]

containment with id h contains node with id`i`

references value array element must be object

9

"j": [
 {
   "resolveInfo": "k",
   "reference": "l"
 }
]

containments value array element must be string

reference with id j points to node with id l, re-binding supported by text k

10 "m": [ null ]

references value array element must be an object

11 "n": true

containments value must be array

references value must be array

12 "o": 12

13 "p": 34.56

14 "q": {}

15 "r": {…​}

16 "s": foo

JSON syntax error

17 "t": undefined
1. We don’t care about serialization verbosity #73
2. Don’t rely on valid, but ambiguous JSON structures #159
3. Allow additional info in serialization #67
4. Include serialization format version in serialization #58
5. Use term `release` instead of `version` for LionWeb? #172
6. Version scheme for LionWeb? #165
7. Should serialization contain a list of used languages? #76
8. Rename M3 Metamodel to Language? #78
9. Repo API: Node representation #33
10. Establish name for entries in serialization/languages? #129
11. Details on builtin language #153
12. Refer to EnumLiteral by key? #128
13. What does Language.version mean semantically? #130
14. Add version property to M3 Metamodel #92
15. Establish term meta-pointer #89
16. Meta-Object Facility, also known as M3 model
17. Repo API: Node serialization #37
18. Require empty members in serialization #59
19. Require empty members in serialization #33
20. Always provide both containment and parent id in serialization #55
21. Discussion on name `concept`
22. Rename `concept` to `classifier` in node serialization #184
23. Keep serialization order between different features? #156
24. Discussion on name `children`
25. rename `nodes.children` → `nodes.containments`? #206
26. Discussion on names `references` and `reference`
27. How to represent annotations in serialization #150
28. Maintain order in serialization of each containment / reference / annotation #157
29. Name of `parent` field in serialization #187
30. How to store invalid text typed at arbitrary places? #62
31. Repo API: Property value encondings #34
32. Repo API: Store additional resolve info? #36
33. Repo API: Represent dangling pointers #35
34. In serialization, `parent` is inverse of either `children` or `annotations` #186
35. Supported built-in primitive types #9
36. Do we allow + prefix for integer property values? #100
37. Don’t specify minimum supported range for integer #149
38. Supported reference targets #57