Heraclitus: elevating deltas to be first-class citizens in a database programming language
Heraclitus: elevating deltas to be first-class citizens in a database programming language
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赫拉克利特：将三角洲提升为数据库编程语言的一等公民
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
D. Jacobs
中科院分区：
文献类型：
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作者：
Shahram Ghandeharizadeh;R. Hull;D. Jacobs
传统的数据库系统为用户提供查询和操作一种数据库状态（即当前数据库状态）的能力。然而，在一些新兴应用程序中，分析“假设”场景以推断更新影响（在提交更新之前）的能力至关重要。示例应用程序包括假设的数据库访问、活动数据库管理系统和版本管理等。赫拉克利特范式的中心论点是通过将增量（代表针对当前数据库状态提出的更新）提升为一等公民，为此类应用程序提供灵活的支持。 Heraclitus[Alg,C] 是一种数据库编程语言，它扩展了 C 以合并关系代数和增量。提供的运算符使程序员能够显式构造、组合和访问增量。最有趣的是 when 运算符，它支持对 delta 的假设访问：表达式 E when &sgr;如果 delta 表达式 &sgr; 的值等于，则产生无副作用表达式 E 将具有的值。应用于当前数据库状态。本文对赫拉克利特范式的哲学进行了广泛的概述，并描述了赫拉克利特的设计和原型实现[Alg, C]。还提出了赫拉克利特范式的独立于模型的形式主义。为了说明 Heraclitus 的实用性，本文深入讨论了如何使用 Heraclitus[Alg, C] 来指定并从而实现活动数据库中规则应用的各种执行模型；这包括文献中提出的著名执行模型，以及最近具有新颖功能的“定制”执行模型。
Traditional database systems provide a user with the ability to query and manipulate one database state, namely the current database state. However, in several emerging applications, the ability to analyze “what-if” scenarios in order to reason about the impact of an update (before committing that update) is of paramount importance. Example applications include hypothetical database access, active database management systems, and version management, to name a few. The central thesis of the Heraclitus paradigm is to provide flexible support for applications such as these by elevating deltas, which represent updates proposed against the current database state, to be first-class citizens. Heraclitus[Alg,C] is a database programming language that extends C to incorporate the relational algebra and deltas. Operators are provided that enable the programmer to explicitly construct, combine, and access deltas. Most interesting is the when operator, that supports hypothetical access to a delta: the expression E when &sgr; yields the value that side effect free expression E would have if the value of delta expression &sgr; were applied to the current database state. This article presents a broad overview of the philosophy underlying the Heraclitus paradigm, and describes the design and prototype implementation of Heraclitus[Alg, C]. A model-independent formalism for the Heraclitus paradigm is also presented. To illustrate the utility of Heraclitus, the article presents an in-depth discussion of how Heraclitus[Alg, C] can be used to specify, and thereby implement, a wide range of execution models for rule application in active databases; this includes both prominent execution models presented in the literature, and more recent “customized” execution models with novel features.