Program

An introduction to the concept of declarative programming.

Saxon-Forms is a (currently) partial XForms implementation developed using Saxon-JS, an XSLT 3.0 run-time written purely in JavaScript. Designed for browsers the mechanics of the XForms implementation such as actions are implemented using ‘interactive’ XSLT 3.0 extensions available with Saxon-JS, to update form data in the (X)HTML page, and handle user input using event handling templates.

Over the last 5 years many NoSQL vendors have relicensed their software, and the landscape is only becoming more tumultuous with several vendors recently playing a licensing game which is akin to Musical Chairs. Developing a new NoSQL database is no small feat, and we must eventually choose some sort of license for our users. We examine what is driving the licensing changes in the wider database community, how they apply to a new entrant to the marketplace, and ultimately ask the question, are we still Open Source?

A multi-billion pound project to provide a national distributed patient-record system for the British National Health Service failed. One person, John Chelsom, recoded it using declarative techniques, and it now running in several hospitals.

The Views project was an outgrowth of the ABC project — the programming language that gave birth to Python. Views was specifically an effort to design a programming environment for the ABC programming language. Its main shortcoming may have been that it was ahead of its time. The Views system has been characterized as a browser avant la lettre; I will argue that it was much more than that.

Declarative programming may not seem to be widespread, but it has been used for several decades in some areas of information technology. Examples are SQL for querying databases, and regular expressions and grammars for text analysis. More recently, domain-specific languages have been used to take advantage of declarative methods, with varying degrees of success. What can we learn from the successful applications of declarative programming? And perhaps more importantly, is there something that failed applications have in common? In this presentation we will look at declarative techniques that are so ubiquitous that nobody notices them anymore. We will also look at two pitfalls that the author has encountered many times: genericity and reification.

In XML Prague this year I presented on a proof of concept grammar parser in XSLT. In this presentation I plan to release an open-source fully compliant Invisible XML parser based on this work. The presentation will demonstrate iXML parsing, some technical details of the implementation, and finish with a short overview of the advantages of this declarative approach of parsing text. I also hope to show how it is possible for the parser to extend itself to other grammar languages.

It has become a trend amongst modern high-performance databases to optimise queries by avoiding interpretation of the query language. They instead opt to compile queries to native machine code which can subsequently be executed directly by one or more CPUs and/or GPUs. Both Saxon and XSLTC have previously demonstrated, albeit by different means, compilation of XSLT and XQuery to Java bytecode which can then be executed by the Java Virtual Machine. To the best of our knowledge, we are the first group to demonstrate the compilation of XQuery directly to native machine code. As part of a research effort to develop a new performant XQuery processor for our poly-store database (FusionDB), we are constructing an XQuery parser which emits LLVM IR (Intermediate Representation), and a JIT (just-in-time) compiler to produce native machine code which is then executed. In this paper we review the current approaches to native query compilation, detail our challenges and progress in building a modern XQuery parser, and our use of LLVM for compiling XQuery to native machine code. We also consider how we might exploit LLVM's low-level IR optimizations to improve query performance.

With the meteoric rise of HTML5 and the slow demise of XHTML, simple in-browser WYSIWYG editors for producing XML documents have all but disappeared. Today, there are numerous Open Source JavaScript components for simple in-browser editors (e.g. CKEeditor, Editor.js, Quill, TinyMCE, etc.) that produce documents in a subset of HTML5. Likewise, there are free and commercial SaaS offerings that edit and publish reStructuredText or Markdown documents from within the browser (e.g. readthedocs.org, gitbook.com, and mkdocs.org). The lack of simple in-browser XML editors, is likely driven by several factors: 1. The complexity of offering a full XML editor. One of the advantages of XML is its flexibility, an author can arbitrarily decide on their document structure, and element and attribute names, however this adds complexity to any such editor. Conversely schema languages for XML that limit that flexibility by enforcing a certain document grammar, then require extra parsing and validation steps by the editor. 2. A decrease in XML processing support within the browser itself. 3. A perceived reduction in what constitutes an acceptable level of re-use and presentation for technical documentation. When compared to HTML5, Markdown, and reStructuredText, we believe that there are still key advantages that can be exploited by using XML for technical documentation. For the purposes of authoring and publishing the documentation for FusionDB Server, we examined several markup formats but ultimately settled on LwDITA. We intend to show that LwDITA occupies an optimum position, it allows us to reap the benefits of XML, whilst remaining simple enough to allow us to develop a simple and compliant in-browser editor. Whilst we acknowledge that there are a handful of existing commercial and/or enterprise offerings which include in-browser XML editors (e.g. Oxygen XML Web Author, easyDITA, Xopus, etc.), they are in themselves very comprehensive and complex products with accompanying costs. Rather, we intend to both discuss the construction of, and demonstrate, our in-browser LwDITA editor as an intentionally simple solution for editing technical documentation.

Notations can affect the way we think, and how we operate; consider as a simple example the difference between Roman Numerals and Arabic Numerals, where Arabic Numerals allow us not only to more easily represent numbers, but they also ease manipulations of numbers and calculations with them. One of the innovations of the World Wide Web was the URL. In the last 30 years, URLs have become an ever-present element of everyday life, so present that we scarcely even grant them a second thought. And yet they are a designed artefact: there is nothing natural about their structure -- each part is there as part of a design. This talk will look at the design issues behind the URL, what a URL is meant to represent, and how it relates to the resources it identifies, and its relationship with representational state transfer (REST) and the protocols that REST is predicated on. The talk will consider what mistakes, if any, were made, and with hindsight how if at all the design could have been improved. While it is too late now to change the design of URLs, we will consider what the lessons are that we can draw from their design to direct the future designs of notations.

This paper demonstrates how quality control infrastructure can be generated from a single requirements document. Taken from a recent project that is now being used in production at a large journal publisher, it discusses some of the challenges faced and techniques used when generating Schematron, XSpec tests, XML grammar checks, and documentation. The project set out to implement quality control requirements for journal articles using Schematron. In pursuing this objective, the project also created quality control infrastructure for Schematron itself that streamlines the process for incorporating iterative changes to requirements. The techniques used in this project and described in this paper may be generally applicable in other projects.

Applications that analyze and process natural language can be used for things like named entity recognition, anonymization, topic extraction, sentiment analysis. In most cases, these applications use the plain text of a document, and may add or change markup. This causes problems when the original document already contains markup that must be preserved. The text to be analyzed may run across markup boundaries, and newly generated markup may lead to unbalanced (non well-formed) structures. This presentation shows how the Separated Markup API for XML (SMAX) can be used to apply natural language processing to XML documents. It preserves the existing document structure and allows for balanced insertion of new markup. A demonstration will be given of the use of SMAX for extracting and marking references in legal documents. This Link eXtractor was built for the Dutch center for governmental publications. SMAX and Simple Pipelines of Event API Transformers (SPEAT) will be available as open source software at the time of Declarative Amsterdam.

The Text Encoding Initiative (TEI) is a vast, long standing and widely used encoding standard, covering different areas in the humanities. High quality documentation with many examples and active discussions on the rationale behind the available elements and attributes and their intended use are among the many qualities of the TEI. The TEI presents itself as guidelines, trying to cover as many areas and use-cases in the humanities as possible. The TEI is also designed to be customized for use in specific situations. Customization is achieved via a "One Document Does it all" (ODD). An ODD offers a mechanism to override, restrict, eliminate and extend (parts of) the guidelines in a documented way. ODD can be seen as a powerful abstraction layer from which validation, documentation, but also processing models can be generated. A nice, but complex feature of ODD is that they can be chained, enabling you to have focused ODD's and to promote reuse. In my work on corpora and dictionaries at the Fryske Akademy ODD is the basis from which I generate XSD, configuration, SQL, Java, bind.xml etc. In my presentation I will show you how we benefit from ODD in for example editing and publishing solutions, our goal being to enhance tool development and interoperability through standardization. Outline of the presentation: 1. ODD - explanation and background - chaining - generation 2. Usages - corpora - dictionaries - lexicons - interoperability 3. editing - oXygen: validation and customizing author mode 4. The future - processing model and TEI Publisher

NCL is the declarative programming language used to develop TV applications in IPTV systems and Terrestrial TV standardized by ITU[1] and Brazilian TV Forum, respectively. Its main characteristics are support: defining temporal synchronization among media assets and viewer interactions; layout reuse facilities ( and ); support multi-device presentation; scripts in the light-weight and embeddable language Lua; and an API for building and modifying applications on-the-fly called NCL editing command. This talk briefly introduces NCL, highlights its recent advances and discuss the future of the language.

Although there is at least one parser generator that targets XSLT, this talk is about hand-written parsers. Some difficulties will be described, along with mitigations. Some techniques made possible by XSLT 3 will be described and some examples given. Attention to debugging and testing is also given. The techniques have much wider application than formal parsing, and it turns out to be both useful and fun.

We introduce Rumble, a query execution engine for large, heterogeneous, and nested collections of JSON objects built on top of Apache Spark. While data sets of this type are more and more wide-spread, most existing tools are built around a tabular data model, creating an impedance mismatch for both the engine and the query interface. In contrast, Rumble uses JSONiq, a standardized language specifically designed for querying JSON documents. The key challenge in the design and implementation of Rumble is mapping the recursive structure of JSON documents and JSONiq queries onto Spark's execution primitives based on tabular data frames. Our solution is to translate a JSONiq expression into a tree of iterators that dynamically switch between local and distributed execution modes depending on the nesting level. By overcoming the impedance mismatch in the engine, Rumble frees the user from solving the same problem for every single query, thus increasing their productivity considerably. As we show in extensive experiments, Rumble is able to scale to large and complex data sets in the terabyte range with a similar or better performance than other engines. The results also illustrate that Codd's concept of data independence makes as much sense for heterogeneous, nested data sets as it does on highly structured tables. Abbreviations used in this presentation: CLI: Command-Line Interface CSV: Comma-Separated Values DAG: Directed Acyclic Graph (a graph with no directed cycles, also known as dependency graph) ETL: Extract-Transform-Load, to import data in a database FLWOR: for-let-where-orderby-return (pronounced as 'flower') HDFS: Hadoop Distributed File System, it is an open-source framework for storing very large datasets on a cluster. HTTP: Hypertext Transfer Protocol, the basis of the Web JSON: JavaScript Object Notation RDD: Resilient Distributed Dataset, Spark's data primitive ROOT: CERN's native format for high-energy physics data. S3: Simple Storage Service, Amazon's cloud storage service SQL: Structured english Query Language UDF: User-Defined Function

XML Resolvers are a core extension feature in XML parsers and other applications in the XML stack. They allow you to transparently satisfy requests for DTDs, schemas, stylesheet modules, etc., with local copies of those resources. This offers improvements in both performance and security. XML Resolver 3.0, available in Java and (soon!) C#, provides full support for the XML Catalogs standard and a broad range of features designed to make deploying and using catalog-based resolution faster and easier. This talk will highlight the new features of the resolver including:Dynamic catalog construction with caching.Automatically loading catalogs from extension modules (jar files or assemblies).Improved support for resources distributed in extension modules. Handling http: and https: entries transparently. Validation of catalog files. Namespace-based resource discovery by indirection through RDDL documents.

Declarative approach to routing requests in eXist-db A brief introduction into the status quo, followed by a presentation of a new approach to declaratively design APIs and route requests with examples for several use cases. Introduction I will explain the basics of routing in general. After that, we will have a look at the status quo of routing requests in eXist-db. In particular using rest, RestXQ and the controller.xq and their pros and cons. - rest  - has some quirks  - does not encourage RESTful interface best-practices  - can be hard to secure - restXQ  - route handlers can be somewhere in a package  - can lead to duplicate code for multiple output formats  - parameter handling authentication and error handling is left to the user - controller.xq  - can be hard to secure  - parameter, authentication and error handling is left to the user  - complex controllers can get hard to read  - can only pass strings as parameters to handlers History Because of said limitations of all routing options on exist-db I made several attempts to come up with a better solution that maps a route to a function. 2019 I had a series of small breakthroughs and a working prototype that roughly modelled after the express router known from nodeJS. By mid 2020 Wolfgang Meier expressed the need for a better routing option to use with TEI-publisher. I showed him what I got and he ran with it. He had the brilliant idea to implement the OpenAPI standard and thus created a router where you first create the documentation. You declare which routes exist and what they expect and return. In this configuration you also set things like headers, mime-types and more. This ongoing collaboration is now part of e-editiones, the same society that governs TEI-publisher. Hands-On At the beginning we will have a look at an example JSON file that declares a simple API of an exist-db package. 1. Using a test page created from our declaration 2. Looking at the JSON file itself Then we will create a new route that will output different formats like (HTML, XML, JSON, CSV). I will show how to set arbitrary headers per route, in a handler function, dynamically, for cacheing and also using a middleware for all routes. To round things up, how to secure routes with cookies and basic auth, how to handle authorisation of requests and how to use a custom authentication method. What's next? What are our medium and long-term goals and how can you contribute.

We transform DITA to HTML in the browser via a Single Page App (SPA). Our product GUI is also an SPA – Why not put our content directly in the GUI? This talk shows the advantages of dynamic transforms, and how we use that technique to extract subsets from the single source and display them in the product.

Audio software, and particularly digital signal processing, is an application domain where the imperative, object oriented programming model dominates. In part, this can be justified by the realtime constraints that underly the domain, and that C/C++ has historically dominated the high performance native software landscape. But this is not without cost: the high barrier to entry prevents developers from trying to write audio software, and the industry spends far more time than needed to deliver new products.  In this talk, we'll look at some of the complications that come from writing low level native audio software in C/C++ with an imperative, object oriented model. Then we'll reframe the conversation to show why a functional, declarative approach may be fundamentally more fitting for the problems we want to tackle when writing new audio software. Finally, I'll introduce Elementary Audio: a new JavaScript runtime for writing realtime, native audio applications with a functional, declarative API. We'll see how Elementary applies the declarative model to audio software, and then finish with a detailed example of a small drum synthesis library written in Elementary.

People working with large XML vocabularies often face the task of upgrading to a new version [1]. Ideally such are guided with a specification of how to map the components of an XML instance to the new version of the vocabulary. SchemaCom was created to assist situations where such a specification is not available. It highlights the differences (and similarities) between the constituent content models in the respective vocabularies, this information can then guide the analysis necessary to specify the missing mappings and can be applied without loss of generality between schemas representing different vocabularies (as opposed to different versions of the same one). A distinguishing feature is the delivery of the user interface as an XForm.

'Invisible XML' ('ixml') is a method for treating non-XML information as if it were XML; it was proposed by Steven Pemberton in 2013. The basic idea is straightforward: a context-free grammar is used to describe the structure of the information, annotations in the grammar specify how the raw parse tree of a sentence in the language described by the grammar is to be represented into XML, and an ixml parser uses the grammar to parse the non-XML document into an XML form. This allows all the tools of the XML toolbox to be applied to the data: XQuery and XSLT for general processing, XForms for creating user interfaces to the data, XML schema languages for validation, and so on. Aparecium is an ixml parser written in XQuery and XSLT, as a library of functions callable from XQuery and XSLT. (The name is a reference to a spell in the Harry Potter novels, which makes invisible writing visible.) When used to parse external resources, Aparecium can be thought of as a replacement for the standard doc() function which can read non-XML data and deliver it as XML; it can also be used to parse strings which obey a context-free grammar, such as CSS style specifications, XSLT pattern expressions, SVG path expressions, and so on. The latter makes Aparecium useful for handling XML formats which use micro-grammars for some portions of documents. For simplicity, Aparecium is implemented as a pipeline of processes. First the extended BNF notation allowed in ixml grammars is translated to an equivalent unextended BNF. This grammar is then used by an Earley parser to parse the input; the result is a large set of 'Earley items' describing various aspects of the parse. From the set of Earley items, Aparecium then constructs a 'parse-forest grammar' describing the set of parse trees in the input. As a final step, a parse tree is extracted from the parse-forest grammar and returned to the caller. Alternate interfaces may be used to specify that the parse-forest grammar should be returned, instead; this may be helpful in cases of ambiguity, since it allows the caller to study the ambiguity and in some cases to extract the preferred parse tree. In some cases the caller will have the grammar in the non-XML form described in the ixml specification; in others, the grammar will be available as an XML document; sometimes the caller will have a URI for the grammar. The input may similarly be available either as a string or as a URI. Aparecium provides distinct calls for each of these situations, to simplify the use of Aparecium in constructing applications. The talk will briefly describe the current status of Aparecium implementation and (the gods willing) show a simple demo; it will conclude with a discussion of some next steps in the work on Aparecium and in the development of broader support for invisible XML.

Front-end web development is rooted in two declarative languages (HTML and CSS) and one imperative language (JavaScript) that can be written in a functional style. Front-end web development is also noted for contentious and ever-shifting gender dynamics – one year HTML and CSS are “for girls” and “not real programming,” another year it's JavaScript that's looked down upon. In this talk, we'll look at the history of front-end development through the twin lenses of gender and declarativity. Along the way, we'll see how gendered programming trends boosted the adoption of popular frameworks – and led to the quiet death of others. We'll get real about the social forces that have affected the credibility and “approachability” of declarative methods in front-end, and talk about how these same forces might play out in other declarative projects.

Despite its many warts and wrinkles, SQL is undeniably a declarative success story. Teaching declarative thinking is often impeded by the procedural mindset of students originating from their early training almost exclusively in imperative programming languages. While SQL databases are optimized for executing SQL, students tend to write inefficient and clumsy code using disputable so-called “procedural extensions”. A few typical examples will be presented. While a limited kind of declarative constraints are supported in SQL, implementations generally fall short of the potential of database-wide declarative constraints. Some notions are illustrated by looking at declarative referential integrity, triggers as a poor substitute and an experimental RDBMS called “Rel”. As a concluding impulse for discussion, the presumed waste of talented declarative minds by the overpowering imperative bias in teaching is addressed.

The vision for a semantic web is over 20 years old, yet so little of our internet is currently using linked data. Where did it go wrong, and what can we do to revive this dream? Atomic Data is a modular specification that aims to make the semantic web achievable again through a developer-friendly ecosystem of tools that enable high data interoperability and return ownership back to the user.

Data is an abstraction. In order to transfer it or talk about it, the abstraction has to be represented using some notation. The design of notations is a neglected area of study, yet the designs affect both what you can represent, and what you can do with what is being represented. XML is currently the most suitable and flexible of the available notations for representing data abstractions, and yet it has restrictions and some shortcomings that get in the way of properly representing abstractions. This paper discusses the issues, and reflects on which aspects of XML get in the way of abstractions.

XML is top down oriented. In a DTD, an element type declaration specifies what content the element may contain, but in no way you can constrain in what context that element may be included. In document oriented languages, where mixed content is typical, it is worth looking up. By seeing in what way an element may occur in its potential parent elements one can classify elements. It raises questions like: is it "suspicious" if an element may occur in the mixed content of some elements, and in the element content of others? Is it suspicious if an element that may occur in mixed content has itself element content? What kind of elements occur in a repeatable OR group? What elements can serve as word boundaries? What does a SEQ group "mean"? Two sequence paradoxes will be mentioned, and by taking as an example both the content and the parents of the "paragraph next door" element we will find that what should be the second most used element in any document instance is actually missing in most industry standard markup languages.

ERP and business systems around the world are having to interconnect more today than ever before. Changing one's system to address interoperability can be a disruption and a risk. The four-corner model for document exchange addresses this in an interoperable network by requiring users' network representatives to exchange the semantic content of documents using a single declarative syntax. For business documents, multiple global networks have chosen the OASIS Universal Business Language (UBL) semantic library and XML syntax between access point network representatives. This is a model any industry sector can adopt to introduce successful interoperability into legacy environments.

The Extensible Markup language (XML) provides a way to share information with tagging specific to content domains, rhetorical forms, or other needs. By contrast, HTML markup is evolved synergistically with Web browsers in mind, and the tagging is largely specific to browsers. Although EPUB was (is) based on XML, it's also based on HTML: it uses XHTML for the documents. As a result, there is little to no support for domain-specific markup, and the ebook experience seems unimaginative, constrained by the intersection of Web browsing and content silos. What might happen if there could be communities evolving domain-specific markup for electronic texts? For 3D models or live mathematics, for poetry, for music and musical scores inside books? For context-specific dictionaries and glossaries, for per-chapter tables of contents and wayfinding cards, and so much more. Is there any way to enrich ebook readers in this direction?

In this presentation we want to explore some aspects of the XProc 3.0 language that could be considered as declarative, while pointing out some other aspects that are potentially not. For doing so we will build the case by looking at some common patterns relevant to pipeline authors. Stating that a programming language is "declarative", is not just a claim in computer science. It also has practical consequences. It is generally understood that declarative programming languages are easier to use and do allow people to solve problems in a shorter amount of time compared to other programming paradigms. Claiming that a programming language would be "declarative" implies that its use has commercial advances over other approaches to solve the same problem. The question whether XProc 3.0 is a declarative language is, to our knowledge, rarely addressed. Control structures like p:choose or p:try in XProc 3.0 might raise doubts about the declarative nature. On the other hand, the level of abstraction in XProc's step infrastructure might at least hint to declarative features. We felt that this tension offered enough motivation to give it some further thoughts. This presentation will not take the computer science theory route. Instead, we will focus on user experience while solving problems with XProc 3.0.

Over the last few years, “Tools for thought” has become a hot concept among software makers. We’ve seeing a surge in note-taking apps and knowledge management tools presenting themselves as TFTs. But there’s a strange paradox here: taken at face value, the phrase “tool for thought” doesn’t have the word ‘software’, ‘computer’ or ‘digital’ anywhere in it. It sounds like an idea that belongs to philosophy and cognitive science department, rather than computing. How and when did it become intertwined with computers? What are we to make of all the software upstarts identifying with this movement? And how can we push beyond them into a new generation of computational tools for thought?