# Ann: A domain-specific language for the effective design and validation of Java annotations

## TL;DR

This paper introduces Ann, a domain-specific language and Eclipse tool for designing and validating Java annotations, enabling explicit modeling of complex annotation dependencies and constraints, demonstrated with Java Persistence API annotations.

## Contribution

The paper presents Ann, a novel modeling language and tool that enhances Java annotation design and validation, addressing Java's native limitations and supporting complex dependency constraints.

## Key findings

- Ann effectively models complex annotation dependencies.
- The tool detects unsatisfiable constraints among annotations.
- Applied to JPA annotations, Ann reveals rich semantics not supported by Java.

## Abstract

This paper describes a new modelling language for the effective design and validation of Java annotations. Since their inclusion in the 5th edition of Java, annotations have grown from a useful tool for the addition of meta-data to play a central role in many popular software projects. Usually they are not conceived in isolation, but in groups, with dependency and integrity constraints between them. However, the native support provided by Java for expressing this design is very limited. To overcome its deficiencies and make explicit the rich conceptual model which lies behind a set of annotations, we propose a domain-specific modelling language. The proposal has been implemented as an Eclipse plug-in, including an editor and an integrated code generator that synthesises annotation processors. The environment also integrates a model finder, able to detect unsatisfiable constraints between different annotations, and to provide examples of correct annotation usages for validation. The language has been tested using a real set of annotations from the Java Persistence API (JPA). Within this subset we have found enough rich semantics expressible with Ann and omitted nowadays by the Java language, which shows the benefits of Ann in a relevant field of application.