orc - The Open Registers Compendium
  ===================================

  Copyright (C) 2018-2019, Andy Bennett and Simon Worthington, Register Dynamics Limited.

 1. Introduction

	Open Registers are a way of expressing an authoritative list that you
	can trust. orc is an implementation of the Open Registers data model
	as well as the more specific gov.uk Registers model.

	This repository is an umbrella for a variety of tools that work
	together to implement various parts of the model:

	+ chicken/orc - A full, persistent, merkle tree backed implementation of
	                Open Registers.

	The files in this repository are distributed under a range of
	licenses. However they are, in general, free to use and modify as long
	as you agree to the terms. Please see the LICENSE files in each
	directory for more information.

	Note: Should you have any trouble in setting up and using these tools,
	please feel free to contact me, Andy Bennett at
	andyjpb@register-dynamics.co.uk.


 2. Installation

	Building the tools in this package requires GNU Make and a recent
	CHICKEN Scheme.

    2.1. Building from git

            Build and install the orc egg for CHICKEN Scheme thus:

            $ cd chicken/
            $ chicken-install

    2.2. What gets installed

          + CHICKEN Scheme library egg

            The library contains the necessary functions to read Registers,
            store them persistently, update the entries in the Register,
            and compute proofs and digests on the data.

          + `orc` command line tool

            The command line tool exposes the functionality of the library
            on the command line. The tool can read from either Register
            Serialisation Format (RSF) files or orc internal databases,
            and can list and modify Register entries and items.

 3. Usage

  The library can be included in a CHICKEN Scheme environment by using
  `(use orc)`, which will bring the exported API into scope.

  3.1 Backing stores

  All calls to library methods must be made in the context of a
  'backing store'. This is an internal database type the orc uses to
  store and manipulate Registers.

  A backing store can be opened with `open-backing-store` which will
  either open an existing file or create one if it does not exist. If
  the backing store is new, it must also be initialised with
  `initialise-backing-store`. Stores can also be created and initialised
  automatically by passing the `-S` option to the command line tool.

  Once a backing store has been opened, library calls can be made inside
  a call to `with-backing-store`.

      (use orc)
      (define my-backing-store (open-backing-store "my.backing-store"))
      (with-backing-store my-backing-store (lambda ()
        (for-each display (list-registers))))

  3.2 Registers

  New Registers can be created using `make-register`, which takes an internal
  name to associate with the new Register.

  Registers in a backing store can be listed with the `list-registers`
  command. This will return a list of Register objects that can be passed
  to other functions, along with the internal name. Individual Registers can
  also be opened directly by passing their internal name to `open-register`.

  Register objects represent a specific version of a specific Register. For
  this reason, any methods that modify a Register also return a new Register
  object representing the new version. This new object must be used from
  this point onwards to make further modifications to the Register. Edit
  functions will fail and complain if an old Register version is used.

  An optional version number can also be passed to `open-register` which
  opens the Register at that version. This is useful for examining the data
  at a previous time.

  3.3 Records

  A Register entry is an association between a key and some values. Each
  key is unique but it can be associated with multiple values at once if
  desired. A Register contains all of the entries that have ever been
  written to it, but not all of them are current.

  Entries exist in one of two regions – the system region or the user
  region. The system region contains Register metadata such as its schema
  while the user region contains the actual data in the Register.

  A record is an entry in the Register that is current – there is no more
  recent entry with that specific key. Records can be listed for a Register
  with `register-records`. Each record can be interrogated using the
  `entry-region`, `entry-key`, `entry-ts` (timestamp) and `entry-items`.

  Records for a given key can be looked up with `register-record-ref`.
  Key objects can be made using `make-key` or `string->key`, and also
  come with eqaulity and comparison operators.

  Entries can be created using `make-entry`, which takes values for all
  the metadata attributes and a list of items. Newly created entries must
  then be passed to `register-append-entry` to add them to the Register.

  3.4 Items

  An item is the actual unit of data in a Register entry. Each entry can
  have multiple items. An entry with zero items is valid but is considered
  to be 'deleted' and will not be returned by `register-records`.

  Items are not contained within an entry – they exist in a separate space
  and are linked to by an entry through an item reference. The reference
  is normally the SHA256 digest of the item contents.

  Items are retrieved from an entry using `entry-items`. Item references
  can be retrieved using `item-item-ref` and the content through `item-blob`.

  Items can be created using `make-item`. Newly created items must then
  be passed to `register-add-item` to add them to the Register. This must
  happen before any entries that contain them are added.

  3.5 Register Serialisation Format (RSF)

  An RSF file contains the entire contents and history of a Register.
  Registers can be loaded from RSF files using `read-rsf`, which will read
  an RSF file from `(current-input-port)` and add it to the backing store
  with a passed internal name.

  There is not currently any support for writing to RSF files.

  3.X Command line tool

  The `orc` command line tool can be invoked with the `--help` switch
  to print full usage information.

 4. Compatibility notes

 5. What's next?

	First and foremost, enjoy the tools and use and extend them to build
	your own things for processing register data.

	Please feel free to send tools that you build with orc so that they
	can be integrated and distributed with this package.

	Suggestion, extensions and patches to orc are welcome.

	If you have any questions or problems (even the slightest problems, or
	the most stupid questions), then please feel free to get in touch with
	me directly using the addresses above. I will try to help you, get you
	going or point you in the right direction.