loro/docs/Glossary.md

Glossary

Name	Meaning	Note
DAG	Directed Acyclic Graph	The changes in Loro form a DAG. The relationship is expressed by deps field.
RLE	Run Length Encoding	We not only use it on the encoding, but also in the vec and tree.
Change	A merged batch of ops
Frontiers	The DAG nodes that no one has dependencies on them	They can be represented by a series of id
Op	Operation
State (of a Container)	The	In the code, the state most refers to the visible state to users. For example, the text string of a text container, the key value pairs in the map container
Effect (of an Op)	How the op affect the state	We use CRDT to calculate the effect (obviously)
Tracker	A special data structure to calculate the effects
Container	A unit of CRDT data structure
Content	Content of an Op
ID	A global unit id for an Op	It has the structure of {clientId, counter}
Counter	The second field inside ID
Lamport	Lamport timestamp
Span	A series of continuous things
Causal Order	The order of happen-before relationship	The DAG expresses the causal order of the changes
VV	Version Vector	In code, it has exclusive end, VV {0: 8} means the last op id of client 0 is 0-7

RLE

We not only use RLE on the encoding, but also in the vec and tree.

i.e. the elements can be merged, sliced and have lengths. We call the element with length of 1 as atom element (cannot be sliced).

We use a Rle trait to express it. So Op, Change, elements inside RleTree all implement Rle. This gives us a compact way to represent the mergeable elements.

Container

Each op is associated with one container. Different CRDT algorithms use different types of containers. There are hierarchical relationship between containers, but they cannot affect each other

Convention

• There are methods like id_last, id_end, lamport_last, lamport_end. last refers to the last one, but end refers to the exclusive end of a range. For example, OpSpan ranging from 0-0 till 0-8 has id_last of 0-8 and id_end of 0-9