@c  This document is part of the Liza Data Collection Framework manual.
@c  Copyright (C) 2017 R-T Specialty, LLC.
@c
@c    Permission is granted to copy, distribute and/or modify this document
@c    under the terms of the GNU Free Documentation License, Version 1.3
@c    or any later version published by the Free Software Foundation;
@c    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
@c    Texts.  A copy of the license is included in the section entitled ``GNU
@c    Free Documentation License''.

@node Design
@chapter Design & Architecture

Liza is fundamentally a data collection framework@mdash{
  }a fancy form for collecting, validating, and lightly processing
  user data.

The main components of the system are:

@table @strong
  @cindex Assertions
  @item Assertions
  Basic validations against bucket data,
    producing errors and manipulating control flow.
  Invokes triggers to manipulate the UI and document.
  Assertions are compiled from Program sources.
  @xref{Assertions}.

  @cindex Bucket
  @item Bucket
  The key/value store into which all document data are stored.
  Supports staging and rollback of data,
    processing deltas,
    and provides hooks that drive the rest of the system.
  @xref{Bucket}.

  @cindex Client
  @item Client
  Basic logic for navigating between steps,
    prompting for user actions,
    display help text and basic document data,
    communicate with server,
    etc.
  @xref{Client}.

  @cindex Data API
  @item Data API
  Declarative abstraction for accessing and processing remote data
    (e.g. a RESTful service).
  @xref{Data API}.

  @cindex Developer Dialog
  @item Developer Dialog
  Renders information about the system for debugging the client.
  Can monitor the bucket, assertions, classification results, and
    provides other useful features.

  @cindex Predicate
  @item Predicate System
  Processes classification data from external classifiers to determine
    applicability of specific questions.
  These data are used to determine what assertions are performed,
    what questions and groups display,
    and more.
  @xref{Predicate System}.

  @cindex Program
  @item Program
  Internal representation of the Program with delegation of events to
    the assertion system.
  Contains compiled representation of all steps, groups, questions,
    assertions, metadata, and others.
  @xref{Program}.

  @cindex Program, User Interface
  @cindex User Interface, Program
  @item Program UI
  Rendering of elements specific to Programs,
    such as steps, groups, and questions.
  This is the equivalent of an HTML form.
  Directly monitors the bucket to perform UI updates.
  @xref{Program UI}.

  @cindex Program, XML
  @item Program XML
  The source code for a Program, in XML format.
  @xref{Program XML}.

  @cindex Server
  @item Server
  Provides REST API for serving Programs; saving data;
    revalidating, filtering, and recalculating data;
    and other types of processing.
  Code is shared with the client,
    ensuring identical behavior for appropriate behaviors.
  @xref{Server}.

  @cindex Type Validation
  @cindex Validation, Type
  @item Type Validation
  Validates and formats bucket values for specific field (question)
    types.
  For example, a date field must be in a recognized date format,
    and will be normalized for display.
  @xref{Validation}.
@end table

More information about each can be found in their respective chapter/section.