title: Data Encoding
role: manual
tags: #api #manual #reference #zettelstore
syntax: zmk

The data encoding represents the zettel as a special [[symbolic expression|00001012930000]].
In contrast to the similar-looking [[sz encoding|00001012920516]], a much simpler structure is used.

If transferred via HTTP, the content type will be ''text/plain; charset=utf-8''.

A full zettel, both metadata and content, is encoded by the list

:::syntax
''(zettel'' [[__Metadata__|#metadata]] [[__Access rights__|#access-rights]] [[__Content encoding__|#content-encoding]] [[__Content__|#content]] '')''.
:::

If you only want to encode the metadata of a zettel, the following format will be used:

:::syntax
''(list'' [[__Metadata__|#metadata]] [[__Access rights__|#access-rights]] '')''.
:::

=== Metadata
Metadata is basically a sequence of key / value pairs:

:::syntax
__Metadata__ **=** ''(meta'' ''('' __Key__ __Value__ '')'' … '')''.

__Key__ **=** Symbol.

__Value__ **=** String. 
:::

Each __Key__ is a symbol, derivied from the metadata key.
The __Value__ is a string containing the value of the corresponding metadata entry.

=== Access rights
This element encodes [[access rights|00001012921200]] of a zettel:

:::syntax
__Access rights__ **=** ''(rights'' Number '')''.
:::

=== Content encoding
The content encoding specifies, how the zettel content is encoded.
Currently, two values are supported: the empty string and the string ''"base64"''.

:::syntax
__Content encoding__ **=** ''(encoding "")'' **|** ''(encoding "base64")''. 
:::

The empty string indicates that the content is not encoded and can be used as is.
''"base64"'' indicates that the content string is Base64-encoded (typically used for binary content).

=== Content
The content of a zettel is always encoded as a readable string.
For binary content, it is first encoded using Base64.

:::syntax
__Content__ **=** ''(content'' String '')''.
:::