IPLD

IPLD (InterPlanetary Linked Data) is a data model and suite of standards for creating decentralized data structures that are universally addressable and linkable across different content-addressed systems. At its core, IPLD provides a way to link content-addressed data—like that stored on IPFS, Git, or blockchains—using cryptographic hashes as immutable pointers. This creates a merkle graph where any piece of data can be uniquely identified and retrieved by its Content Identifier (CID), enabling interoperability between disparate protocols.

The model is built around a simple, flexible format called IPLD Data Model, which supports common types like maps, lists, strings, integers, bytes, and links. These links are the key innovation: they are special values that resolve to other nodes in the graph via their CID. This structure allows for the creation of complex, interconnected datasets—such as the entire history of a Git repository, a blockchain's state, or a decentralized website—where integrity is guaranteed by the underlying hashes. Tools like the ipld library in various languages allow developers to traverse these graphs programmatically.

A primary application of IPLD is within the InterPlanetary File System (IPFS), where it serves as the backbone for representing files and directories. However, its utility extends to blockchain systems like Filecoin and Ethereum, where it can model state tries and transaction receipts. By providing a common language for hash-linked data, IPLD solves the vendor lock-in problem, allowing data to be portable and verifiable across different networks and applications without centralized coordination.

The term IPLD is an acronym for InterPlanetary Linked Data. It was coined by Juan Benet, the creator of the InterPlanetary File System (IPFS), to describe a data model for linking content-addressed information across different distributed systems. The "InterPlanetary" prefix is a nod to the project's ambitious vision of creating a resilient, global-scale data layer for the web, extending beyond a single planetary context. "Linked Data" directly references the core technical concept of creating a web of data connected by cryptographic hashes, similar to how the World Wide Web uses URLs to link documents.

The name was chosen to be evocative and aspirational, positioning the technology as a fundamental building block for a new, decentralized internet architecture. It deliberately echoes the naming of IPFS (InterPlanetary File System), establishing it as a sibling or complementary protocol within the same conceptual family. While IPFS handles file storage and retrieval, IPLD provides the underlying data model that makes this linking possible, acting as the "data" layer to IPFS's "file system" layer. This etymological connection underscores their symbiotic relationship.

Beyond its branding, the term precisely captures the protocol's technical essence. InterPlanetary implies a system designed for high-latency, potentially disconnected environments—a key characteristic of peer-to-peer networks. Linked Data specifies the method: creating immutable, verifiable connections between pieces of data using Content Identifiers (CIDs). This naming convention has helped distinguish IPLD from other data serialization or modeling formats by emphasizing its unique role in creating a unified layer for hash-linked information across protocols like IPFS, Filecoin, Git, and Bitcoin.

IPLD works by representing all content-addressed data as a graph of linked nodes, where each node is identified by a cryptographic hash called a Content Identifier (CID). This creates a Merkle DAG (Directed Acyclic Graph), a structure where data is linked in a way that ensures integrity and enables efficient verification. Any piece of data, from a simple string to a complex file directory, can be modeled as an IPLD node and given a unique, verifiable address derived from its content.

The power of IPLD lies in its interoperability layer, which uses the CID as a universal "link" format. A CID can point to data stored on IPFS, Filecoin, Ethereum, or other blockchains, allowing applications to traverse and resolve links across these disparate systems seamlessly. This is achieved through codecs (like dag-cbor or dag-json) that define how data is serialized, and multihash and multicodec identifiers within the CID that specify the hash function and data format.

Developers interact with IPLD through data models and selector languages. The primary model treats data as JSON-like structures with links, while IPLD Schemas provide a type system for defining and validating these structures. Selectors are expressive queries that traverse the Merkle DAG, enabling efficient fetching of specific sub-graphs of data without needing to download entire datasets, which is crucial for performance in decentralized networks.

IPLD (InterPlanetary Linked Data) is a data model and a suite of standards for creating decentralized, content-addressed data structures. At its core, IPLD defines how to link pieces of data using cryptographic hashes, where the hash of a piece of content acts as its unique, immutable identifier (CID). This creates a Directed Acyclic Graph (DAG) of linked data, where any node can be retrieved and verified by its hash. The model is protocol-agnostic, meaning it can represent data from systems like Git commits, Bitcoin blocks, and IPFS files using a unified set of tools.

The primary data format within IPLD is IPLD Data Model, which supports common types like maps, lists, strings, integers, bytes, and links. These links are special types that point to other nodes via their Content Identifier (CID). A CID is a self-describing content address that specifies the cryptographic hash of the data, the hash function used (e.g., SHA-256), and a codec identifier (e.g., dag-cbor, dag-json) for interpreting the raw bytes. This allows systems to understand how to decode and traverse the data without prior coordination.

A key concept is the IPLD Selector, a declarative language for traversing specific paths through an IPLD graph. Instead of fetching an entire dataset, a selector allows a client to request only the relevant nodes, enabling efficient partial data retrieval. This is critical for performance in large decentralized networks. Selectors work in conjunction with the IPLD Schema language, which provides a way to define types and constraints for IPLD data, adding a layer of structure and validation similar to a schema in traditional databases.

Developers interact with IPLD through implementations like go-ipld-prime (Go) and js-ipld (JavaScript), which provide libraries for creating, manipulating, and resolving IPLD data. Common operations include creating a Merkle DAG (where the graph's structure is also hashed), resolving a path like /ipfs/QmHash/object/property, or using a block storage interface to put and get data blocks. These tools abstract the complexities of multihash, multicodec, and multibase encoding that underpin the CID specification.

The power of IPLD lies in its interoperability. Because it provides a common lingua franca for hash-linked data, a Bitcoin block header, an IPFS file, and a Git commit can all be represented and traversed using the same set of IPLD tools. This enables powerful cross-protocol applications, such as proving the state of a blockchain within a smart contract on another chain or creating complex, versioned datasets where every change is immutably recorded and linked.