Data Structures

Twine data structures

Twine uses IPLD to encode its data. There are two data structures: Pulses, and Chain metadata.

Pulses are logically grouped as chains, which act as proxies for ownership. Generally, a chain is produced for a single purpose or use case by a single process and owner. Every pulse of every chain is also linked (via hash-linking) to pulses of other chains, thus forming the larger Tapestry. Chain metadata stores meta information about the construction of the chain, including the public key for provenance verification.

Hash-linking of the data structures is facilitated by the process of content addressing and CIDs. With content addressing, data is referenced by its hash instead of its location using a special identifier called a Content ID (CID). A CID is constructed using the hash of serialized data, meta-information about the serialization method, hash algorithm, format, and version of the CID itself. This self-descriptive CID is used as both an identifier for retrieval of the original data, as well as a checksum to verify its integrity. Since CIDs contain a hash of the data, they can be used for the purposes of hash-linking.

Content addressing and CIDs were established as part of the distributed peer-to-peer filesystem IPFS, however IPFS is not necessary for Twine data.

Both Pulses and Chain metadata follow a similar outer structure. What distinguishes them is the type of their `content` property.

type TwinePulse struct {
    content PulseContent
    signature String
} representation map

type TwineChain struct {
    content ChainContent
    signature String
} representation map

Signatures

Signatures are represented as a string type which encodes a Compact Javascript Web Signature JWS.

Example Compact JWS

"eyJhbGciOiJFUzI1NiJ9.FECjYMLfBcaarQShFsVVcV3h12vG9Aw2JN5yNptUodLAQV3mfxSgwqdO-VQStLeTRdZDon4YXVGtcgZ_aLzbEqw1.3xZ-2BxejyxinNugtmmm5bo4LuuymNk0KRILsNMluYXjgKWLJRI9EO_MbUnBGiLjAOg16PV6CGrjYDNwAzzbkQ"

Mixins

Twine structures make use of a Mixin type which is used to store connections between chains.

type Mixin struct {
    chain Link
    value Link
} representation map

Pulses

Pulses are the data structures that chain together to create the tapestry. They are the structures that carry payloads and are used to append updates.

Schema

type PulseContent struct {
  specification String
  chain Link
  index Integer
  links [Link]
  mixins [Mixin]
  source String
} representation map

Example JSON

Chain Metadata

Chain Metadata structures store information about the chain as a whole. They must be retrieved in order to verify the signatures of Twine data structures.

Schema

type ChainContent struct {
  specification String
  key JWK # https://www.rfc-editor.org/rfc/rfc7517
  links_radix Integer
  meta Map
  mixins [Mixin]
  source String
} representation map

Example JSON