Fill in section about the data model

README.md

@@ -488,7 +488,50 @@ Clojure functions serialized to this type will have their arguments and return
 value exactly match the types specified and will not perform any serialization
 or deserialization at their boundaries.
 
-### TODO Data Model
+### Data Model
+In addition to the macros and functions provided to build a Clojure API for
+native libraries, facilities are provided for taking data and loading all the
+symbols specified by it. This can be useful if a library provides (or an
+external provider maintains) a data representation of their API, as Clojure data
+to represent it may be programmatically generated from these sources.
+
+The data to represent an API is a map with the following form:
+
+```clojure
+(def strlen-libspec
+  {:strlen {:type :function
+            :symbol "strlen"
+            :function/args [::ffi/c-string]
+            :function/ret ::ffi/long}})
+```
+
+Each key in this map represents a single symbol to be loaded. The value is a map
+with at least the keys `:type` and `:symbol`. These are the currently recognized
+types:
+
+- function
+- varargs-factory
+- const
+- static-var
+
+Each one has its own set of additional keys which can be added to the map. Both
+`function` and `varargs-factory` have the three keys `:function/args`,
+`:function/ret`, and `:function/raw-fn?`. The `const` type has `:const/type` and
+`static-var` has `:static-var/type`.
+
+This data can be passed to the function `reify-libspec`, which will take the
+data and return a map from the same keys as the input map to whatever value is
+appropriate for a given symbol type (e.g. a Clojure function for `function`, a
+value for `const`, etc.).
+
+```clojure
+(ffi/reify-libspec strlen-libspec)
+;; => {:strlen #function[...]}
+```
+
+This functionality can be extended by specifying new types as implementations of
+the multimethod `reify-symbolspec`, although it's recommended that for any
+library authors who do so, namespaced keywords be used to name types.
 
 ## License