Encoding of Sz Metadata

A single metadata (“metadatum”) is represented by a triple: a symbol representing the type, a symbol representing the key, and either a string or a list that represent the value.

The symbol depends on the metadata key type. The value also depends somehow on the key type: a set of values is represented as a list, all other values are represented by a string, even if it is a number.

The following table maps key types to symbols and to the type of the value representation.

Key Type	Symbol	Value
Credential	`CREDENTIAL`	string
EString	`EMPTY-STRING`	string
Identifier	`ZID`	string
IdentifierSet	`ZID-SET`	ListValue
Number	`NUMBER`	string
String	`STRING`	string
TagSet	`TAG-SET`	ListValue
Timestamp	`TIMESTAMP`	string
URL	`URL`	string
Word	`WORD`	string

ListValue = ( String₁ String₂ … String_n ).

Examples:

The title of this zettel is represented as: (EMPTY-STRING title "Encoding of Sz Metadata")
The tags of this zettel are represented as: (TAG-SET tags ("#api" "#manual" "#reference" "#zettelstore"))