Add SQL schema

schema.sql

@@ -0,0 +1,33 @@
+-- This is the database schema for PostgreSQL.
+
+begin;
+
+create table collection (
+       path varchar primary key not null,
+       parent_path varchar references collection (path));
+
+create table item (
+       name varchar primary key not null,
+       tag varchar not null,
+       collection_path varchar references collection (path) not null);
+
+create table header (
+       key varchar not null,
+       value varchar not null,
+       collection_path varchar references collection (path) not null,
+       primary key (key, collection_path));
+
+create table line (
+       key varchar not null,
+       value varchar not null,
+       item_name varchar references item (name) not null,
+       timestamp timestamp not null,
+       primary key (key, item_name));
+
+create table property (
+       key varchar not null,
+       value varchar not null,
+       collection_path varchar references collection (path) not null,
+       primary key (key, collection_path));
+
+commit;