Incremental relational lenses

Abstract

Lenses are a popular approach to bidirectional transformations, a generalisation of the view update problem in databases, in which we wish to make changes to source tables to effect a desired change on a view. However, perhaps surprisingly, lenses have seldom actually been used to implement updatable views in databases. Bohannon, Pierce and Vaughan proposed an approach to updatable views called relational lenses, but to the best of our knowledge this proposal has not been implemented or evaluated to date. We propose incremental relational lenses, that equip relational lenses with change-propagating semantics that map small changes to the view to (potentially) small changes to the source tables. We also present a language-integrated implementation of relational lenses and a detailed experimental evaluation, showing orders of magnitude improvement over the non-incremental approach. Our work shows that relational lenses can be used to support expressive and efficient view updates at the language level, without relying on updatable view support from the underlying database.A typical web application is based on a three-tier architecture with user interaction on the client (web browser), application logic on the server, and data stored in a (typically relational) database. Relational databases employ SQL query and update expressions, including projections, selections and joins, which correspond closely to familiar list comprehension operations in functional languages. Relational databases offer data persistence and high performance and are flexible enough for a range of applications. However, the impedance mismatch between database queries and conventional programming makes even simple programming tasks challenging [Copeland and Maier 1984]. Languages such as C# [Meijer et al. 2006], F# [Syme 2006; Cheney et al. 2013], Links [Cooper et al. 2006], and Ur/Web [Chlipala 2015], and libraries such as Database-Supported Haskell [Ulrich andGrust 2015], have partly overcome this challenge using language-integrated query, in which query expressions are integrated into the host language and type system. However, language support for database programming is still incomplete. For example, views are a fundamental concept in databases [Ramakrishnan and Gehrke 2003] that are typically not supported in language-integrated query. A view is a relation defined over the database tables using a relational query. Views have many applications: 1 Information such as the hostname, port, username and password needed to access the database also needs to be provided; this can be included in the database expression or, as here, in a separate configuration file. 2 Such constraints are not currently checked in our implementation, but this is straightforward and an orthogonal concern. Incremental Relational Lenses :5 var albumsLens = lens albumsTable with album -> quantity; var tracksLens = lens tracksTable with track -> date rating;A common workflow within a web application is to extract some view of the data from the database, associate it with a f...

The optics of language-integrated query

“…As a matter of fact, lenses emerged in this context [33] under the umbrella of bidirectional programming. We remark [53] as a recent work in this field, where a practical approach to the view update problem is introduced by means of the so-called incremental relational lenses. Although we still do not know if extending Optica will lead us to contemplate views in the non-standard SQL semantics, we find this research essential to deal with updating optics in an effective way.…”

Replication Package for Article

“…Most of the following characterisations of incremental relational operations are presented in prior work such as Griffin et al [1997], but without detailed proofs; we include detailed proofs in the full version [Horn et al 2018].…”

“…This first table contains the title of the paper, the year it was published as well as the proceedings it is in, while the inproceedings_author table contains an entry for each author on every paper, allowing a single publication to have multiple authors. More information as well as example data is listed in the full version of this paper [Horn et al 2018].…”

“…This is slightly simpler than, but equivalent to, the definition given byBohannon et al [2006a]. The proof that the two definitions are equivalent is provided in the full version of the paper[Horn et al 2018]. Proc.…”

Avoiding unnecessary information loss: correct and efficient model synchronization based on triple graph grammars

“…Various bidirectional transformation (bx) approaches [3,14] for models have been suggested to deal with model (view) synchronization and consistency. Across these different approaches the following are important research topics [13,15,26,[31][32][33]47]: incrementality, i.e., achieving runtime/complexity dependent on the size of the model change, not on the model size, and least change, i.e., keeping the resulting model as similar as possible to the original one while restoring consistency. In this work, we extend synchronization approaches based on triple graph grammars by specific repair rules to increase incrementality and efficiency and to decrease the amount of change that occurs during synchronization.…”