Athena Developer Guide

Athena
Chapter 9 Data dictionary Version/Issue: 2.0.0
Chapter 9
Data dictionary
9.1 Overview
In contrast to the other Chapters in this User Guide, this one does not describe existing functionality,
but rather gives an preview to new functionality that will be made available in a future release. It
describes the role, scope, and implementation of a "Data Dictionary" in the Athena Architecture. It is a
condensation of a snapshot of a separate working document.
9.1.1 Definition of Terms
The term data dictionary is being used in ATLAS as a catch phrase for several related, but distinct
concepts and techniques. We categorize these concepts into three general categories:
• Introspection/Reflection/Object Description/Run-Time Typing
This refers to objects in program memory with the ability to describe themselves in a
programmatic way through a public API such that they can be manipulated without a priori
knowledge of the specific class/type of the object.
• Code Generation
This refers to a process of generating code for performing a specific task from a generic
description/input file.
• Self-Describing External Data Representation (e.g. Data Files)
This refers to external data representations (e.g. file formats, on-wire data formats) which
contain metadata describing the payload of the data file, etc.
Each of these concepts plays a different set of roles in an architecture dependent upon a data dictionary.
NB: Throughout this document we will use the word object without (necessarily)
referring to an actual instance of a C++/Java/other class. A potentially better phrase
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