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 # Design and Data Model
 
-Most of the manual is about how to use Nix.
 This chapter is about the technical principles behind Nix.
 
-It describes each architectural layer and its components in its own section, starting at the bottom with the store layer, then working its way up to the user-facing components described in the rest of the manual.
+## Architecture
+
+Nix consists of hierarchical [layers](https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers).
+
+```
+               [ commmand line interface ]
+                            |
+                            | evaluates
+                            V
+               [ configuration language  ]
+                            |
+                            | evaluates to
+                            |
+              reference     V       build
+[ build inputs ] --> [ build plans ] --> [ build results ]
+          \                 |                 /
+            \               | persisted to  /
+              \             V             /
+              [           store           ]
+```
+
+At the top is the *command line interface*, translating from invocations of Nix executables to interactions with the underlying layers.
+
+Below that is the *Nix language*, a [purely functional programming](https://en.m.wikipedia.org/wiki/Purely_functional_programming) language.
+It is used to compose expressions which ultimately evaluate to self-contained *build steps*, used to derive *build results* from referenced *build inputs*.
+
+::: {.note}
+The Nix language itself does not have a notion of *packages* or *configurations*.
+As far as we are concerned here, the inputs and results of a derivation are just data.
+In practice this amounts to a set of files in a file system.
+:::
+
+The command line and Nix language are what users interact with most.
+
+Underlying everything is the *Nix store*, a mechanism to keep track of build plans, data, and references between them.
+It can also execute *build instructions*, captured in the build plans, to produce new data.
+