Property graphs have reached a high level of maturity, witnessed by multiple robust graph database systems as well as the ongoing ISO standardization effort aiming at creating a new standard Graph Query Language (GQL). Yet, despite documented demand, schema support is limited both in existing systems and in the first version of the GQL Standard. It is anticipated that the second version of the GQL Standard will include a rich DDL. Aiming to inspire the development of GQL and enhance the capabilities of graph database systems, we propose PG-Schema, a simple yet powerful formalism for specifying property graph schemas. It features PG-Types with flexible type definitions supporting multi-inheritance, as well as expressive constraints based on the recently proposed PG-Keys formalism. We provide the formal syntax and semantics of PG-Schema, which meet principled design requirements grounded in contemporary property graph management scenarios, and offer a detailed comparison of its features with those of existing schema languages and graph database systems.

翻译：属性图已达到较高成熟度，多款稳健的图数据库系统以及旨在创建新标准图查询语言（GQL）的持续ISO标准化工作都印证了这一点。然而，尽管存在明确需求，无论是现有系统还是GQL标准首个版本在模式支持方面都较为有限。预计GQL标准第二版本将包含丰富的DDL。为启发GQL开发并增强图数据库系统能力，我们提出了PG-Schema——一种简单而强大的属性图模式形式化描述方法。其特色在于支持多继承的灵活类型定义PG-Types，以及基于近期提出的PG-Keys形式化方法所构建的表达性约束。我们给出了PG-Schema的形式化语法与语义，这些设计遵循基于当代属性图管理场景的原则性需求，并详细比较了其特性与现有模式语言及图数据库系统的异同。