From Data to Data Structures
Hashes are wonderful.
If you hash something you can give that hash to anyone else in the world, anywhere in the galaxy (IP stands for InterPlanetary), they can tell if they have that data and when they send it to you, you're able to verify it was the right data even without trusting that person.
If you think of hashes like URLs, you can pass them around and ask people for them without fixing the place where that data exists into the link the way you do with a URL. This is really powerful, but by itself it's a bit limited.
For one thing, there are lots of hash algorithms, and they keep
getting better. A hash doesn't say what sort of hash it is. We
solved that with something called
which is just a hash that says "I'm a hash of this particular
So now, with multihash, a single identifier can get us any set of binary data (what we call a "Block") from anywhere in the world.
That's data, we've got that covered, but now we need to go from data to data structures.
IPLD is how we go from data to data structures.
We do this with a new link type and a data model.
For links we use a CID. A CID is an extension of
in fact a
multihash is part of a
CID. We simply add a codec to a
that tells us what format the data is in (JSON, CBOR,
Bitcoin, Ethereum, etc). This way, we can actually link between
data in different formats and any link to data anyone ever gives
us can be decoded so that it can become more than just a series
CID is a standard that anyone can implement, even people that have no other interest in IPLD beyond the need for hash links to different data types can use it.
The Data Model
The IPLD Data Model is a bit more conceptual and can be applied to formats that have never considered IPLD.
Consider that every programming language has a library for JSON encoding and decoding. These languages all adapt the JSON data model (types) into the best fit for that language. A "number" in JSON has many potential mappings in different languages, a JSON library has to decide how it is most appropriately represented. Our data model is very similar to the JSON data model, but we add a few more types.
First, we add a link type using CID as our link format. We also add a binary type, which are missing from JSON. We support nothing beyond these and the other types that JSON has already defined quite well.
We then apply this data model to more than just our own formats. We have specifications and libraries for interpreting many formats into this data model. For instance, Bitcoin blocks know nothing about IPLD since they were designed long before IPLD existed. We have a decoder for Bitcoin that presents the data found in a Bitcoin block as the IPLD Data Model.
This provides a consistent interpretation of all formats across all programming
languages in IPLD terms. For instance, Bitcoin data includes hashes to identify
blocks and transactions to form a heavily interlinked blockchain. Bitcoin doesn't
use CID's internally, but when you use an IPLD codec to read Bitcoin data, the
hashes will be normalized to CIDs so we maintain a consistent "link" type that
includes the content address (hash), the hash algorithm (double-SHA2-256) and the
IPLD codec (e.g.
This lets you build data structures that freely link between formats that can be traversed though a normalized data model. Effectively, you can write format agnostic tools for reading, distributing, and persisting all content addressed data. Your custom IPLD data structure, encoded in your chosen IPLD codec, can link to anyone else's IPLD data, arbitrary Bitcoin blocks, Git commits and a universe of content addressed data.