# How Salsa works
## Video available
To get the most complete introduction to Salsa's inner workings, check
out [the "How Salsa Works" video](https://youtu.be/_muY4HjSqVw). If
you'd like a deeper dive, [the "Salsa in more depth"
video](https://www.youtube.com/watch?v=i_IhACacPRY) digs into the
details of the incremental algorithm.
> If you're in China, watch videos on ["How Salsa Works"](https://www.bilibili.com/video/BV1Df4y1A7t3/), ["Salsa In More Depth"](https://www.bilibili.com/video/BV1AM4y1G7E4/).
## Key idea
The key idea of `salsa` is that you define your program as a set of
**queries**. Every query is used like a function `K -> V` that maps from
some key of type `K` to a value of type `V`. Queries come in two basic
varieties:
- **Inputs**: the base inputs to your system. You can change these
whenever you like.
- **Functions**: pure functions (no side effects) that transform your
inputs into other values. The results of queries are memoized to
avoid recomputing them a lot. When you make changes to the inputs,
we'll figure out (fairly intelligently) when we can re-use these
memoized values and when we have to recompute them.
## How to use Salsa in three easy steps
Using Salsa is as easy as 1, 2, 3...
1. Define one or more **query groups** that contain the inputs
and queries you will need. We'll start with one such group, but
later on you can use more than one to break up your system into
components (or spread your code across crates).
2. Define the **query functions** where appropriate.
3. Define the **database**, which contains the storage for all
the inputs/queries you will be using. The query struct will contain
the storage for all of the inputs/queries and may also contain
anything else that your code needs (e.g., configuration data).
To see an example of this in action, check out [the `hello_world`
example][hello_world], which has a number of comments explaining how
things work.
[hello_world]: https://github.com/salsa-rs/salsa/blob/master/examples/hello_world/main.rs
## Digging into the plumbing
Check out the [plumbing](plumbing.md) chapter to see a deeper explanation of the
code that Salsa generates and how it connects to the Salsa library.
