发表机构
LISN Laboratory - University Paris-Saclay, CNRS, INRIA; FORTH Institute of Computer Science（巴黎萨克雷大学 LISN 实验室; FORTH 计算机科学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出一种以带标签有向树为基础结构的新型树数据库模型，其查询语言与树操作均基于函数代数，可在同一框架内支持数据访问与分析，还能实现继承、关联数据库等功能。
AI 中文摘要
我们提出了一种新型数据库模型，其基础结构是带节点标识的带标签有向树。直观来看，树的根节点被视为一个对象（或实体），非根节点是该对象的属性，每个属性的语义由从根节点指向该属性的唯一路径表示。我们将树数据库定义为此类树的集合。数据库中的树可通过本文定义的一组树操作组合生成新树。该模型的查询语言提供两类查询：遍历查询与分析查询。查询（无论是遍历还是分析）始终针对某棵树定义，该树可以是数据库中的树，也可以是通过树操作从其他树派生的树。树操作与查询语言均采用简单函数代数定义，其操作包括函数限制、函数组合、函数配对及集合笛卡尔积。该模型的显著特征在于，遍历查询与分析查询在同一形式框架内定义，且遍历查询实际上是分析查询的构建模块；这与关系模型形成鲜明对比，关系模型中分析查询以SQL分组查询的形式在关系代数外部定义。因此，我们的模型支持在同一形式框架内实现数据访问与数据分析。我们通过以下内容展示该模型的表达能力：（a）该模型如何无缝支持继承；（b）如何在树数据库之上定义一致的关系数据库，其中树数据库作为底层语义层；（c）树数据库如何用作访问和分析关系数据的用户友好型接口。
英文摘要
We propose a novel database model whose basic structure is a labeled, directed tree with node identities. Intuitively, the root of the tree is seen as an object (or entity), the non-root nodes as attributes of the object and the semantics of each attribute is represented by the unique path leading from the root to the attribute. We define a tree database to be a set of such trees. The trees of the database can be combined to produce new trees using a set of operations on trees that we define in the paper. The query language of our model offers two types of queries, traversal queries and analytic queries. A query (whether traversal or analytic) is always defined over a tree, which is either a tree in the database or a tree derived from other trees using tree operations. The operations on trees and the query language are both defined using a simple functional algebra whose operations are: restriction of a function, composition of functions, pairing of functions and Cartesian product of sets. A distinctive feature of our model is that traversal queries and analytic queries are both defined within the same formal framework; and in fact, traversal queries serve as the building blocks for analytic queries. This is in sharp contrast to the relational model, where analytic queries are defined outside the relational algebra, in the form of SQL Group-by queries. Therefore our model supports data access and data analysis within the same formal framework. We demonstrate the expressive power of our model by showing: (a) how our model can support inheritance in a seamless manner, (b) how one can define consistent relational databases on top of a tree database - with the tree database playing the role of an underlying semantic layer and (c) how a tree database can be used as a user-friendly interface for accessing and analyzing relational data.
