=Paper=
{{Paper
|id=Vol-1690/paper91
|storemode=property
|title=Representing RDF Stream Processing Queries in RSP-SPIN
|pdfUrl=https://ceur-ws.org/Vol-1690/paper91.pdf
|volume=Vol-1690
|authors=Robin Keskisärkkä
|dblpUrl=https://dblp.org/rec/conf/semweb/Keskisarkka16
}}
==Representing RDF Stream Processing Queries in RSP-SPIN==
https://ceur-ws.org/Vol-1690/paper91.pdf
Representing RDF Stream Processing Queries in
RSP-SPIN
Robin Keskisärkkä
Linköping University, Linköping, Sweden
robin.keskisarkka@liu.se
Abstract. A number of RDF Stream Processing (RSP) systems have
been developed to support processing of streaming Linked Data, however,
due to the lack of a standard query language they all provide different ex-
tensions. The RSP Community Group1 is in the process of standardizing
the RSP query language (RSP-QL), which incorporates many features
from existing RSP languages. In this paper we present a demo showing
how RSP-SPIN, a SPIN extension for RSP-QL, can be used to encapsu-
late RSP-QL queries as RDF, which can then be used to support serial-
ization into multiple RSP languages. This can reduce the effort required
to produce and maintain queries for RSP benchmarks, since developers
can focus on a single representation per query, and assist developers in
combining or switching between different RSP engines.
Keywords: RDF Stream Processing, RSP-QL, RSP-SPIN
1 Introduction
The amount of data published as online streams is increasing. While the streams
often contain structured or semi-structured data they are often represented using
non-standardized vocabularies and models. Semantic Web (SW) technologies
have the potential to make this heterogeneity manageable; however, traditional
SW technologies are optimized for performance on more or less static data, and
do not scale well when dealing with potentially unbounded streams.
RDF Stream Processing (RSP) has been proposed as a way of bridging the
gap between static and streaming Linked Data [11, 10]. Inspired by technologies
dealing with similar challenges in other domains several RSP engine implementa-
tions have been presented [1–3, 7, 9]. Most of the proposed systems have extended
SPARQL to support the definition of sliding windows over RDF streams.
The RSP Community Group2 is working on defining a standard query lan-
guage for RSP (RSP-QL), and the current version of the abstract syntax and
semantics has already been described in some detail [6, 5]. While the query syn-
tax has yet to be defined in detail the available example queries3 , present a fairly
clear picture of what can be expected in a future standard.
1
https://www.w3.org/community/rsp/
2
ibid.
3
See https://github.com/streamreasoning/RSP-QL/
The diversity of RSP implementations, and their corresponding languages,
makes performance comparisons and switching between engines complicated.
General benchmarks, focusing on different aspects of RSP processing, have been
proposed [4, 8, 12], but comparisons also need to based on, for example, volume,
velocity, necessary query features, and response-time requirements defined in
actual use cases. Developing and validating any type of non-trivial query in a
streaming context is usually both difficult and time-consuming. A major diffi-
culty is that it is often not possible to predict the outcome of a query that is run
against streaming data. Developers often spend considerable time on generating
predicable data streams, or work against recorded data, to be able to compare
results with some expected outcome. Additionally, a query expressed for one
RSP engine is typically not compatible with another, and some validation step
is required for each version of a query.
In this demo we show how RSP-SPIN, an extension of the SPIN Model-
ing Vocabulary4 , can be used to represent RSP-QL queries in RDF. The demo
shows how each query in the CSRBench [4] benchmark can be represented as an
RSP-QL query, and we demonstrate serializers from RSP-SPIN to CQELS [7],
C-SPARQL [2], and SPARQLstream [3].
2 Architecture and Implementation
Sharing and reusing queries is an important aspect in most contexts where people
need to interact with structured data. Many relational databases support some
form of stored procedures, which are ready-made parameterized queries that can
be instantiated by simply providing the required parameters. Storing queries in
such ways has several advantages compared to relying on the users to provide
the queries. For example, stored queries dramatically lower the threshold for
inexperienced users, can be used to protect against query injections, and to
support access control. Stored queries also means that users to not have to have
a detailed understanding of the underlying data models, or have any experience
in crafting queries themselves.
The SPIN Modeling Vocabulary and the SPIN API was developed in part to
provide this functionality for Semantic Web applications. SPIN allows queries to
stored as RDF, and enables the representation of parameterized query templates,
where query variables can be bound to specific values at runtime.
RSP-SPIN extends the functionality of SPIN to model RSP-QL. Since RSP-
QL is based on SPARQL the number of changes made to the base model of SPIN
is small, and most changes simply involve adding the appropriate properties,
classes, and keywords to support the additional concepts introduced in RSP-
QL. This means that compatibility with standard SPIN can be maintained.
RSP-SPIN and the RSP-SPIN API are released as open source5 . The current
version has excluded a some features that have been up for discussion in the
RSP Group, which have yet to be discussed in sufficient depth. In particular the
4
https://www.w3.org/Submission/spin-modeling/
5
https://github.com/keski/rsp-spin/
excluded features include blank nodes for named graphs, and temporal patterns
for Complex Event Processing.
The user interface provided for the demo can be seen in Figure 1. The queries
are represented as RSP-SPIN, which can be serialized into any of the supported
query languages. Activating the RSP-SPIN view displays the underlying RDF
model. The user interface does not support user-defined parameters for tem-
plates, but this is demonstrated in the predefined queries and on the RSP-SPIN
homepage6 .
Fig. 1. The user interface with a CSRBench query loaded. The supported formats for
RSP-SPIN queries are CQELS, C-SPARLQ, SPARQLstream, and RSP-QL.
Switching between views displays the current query in different formats. The
user can pick one of the predefined queries available in the drop-down menu at
the bottom, containing the full set of CSRBench queries. The list also includes
a few examples that illustrate the expressivity of RSP-QL and how the CQELS,
C-SPARQL, and SPARQLstream serializers handle unsupported RSP-QL fea-
tures. User defined queries can be parsed from any view containing a parse
button. Pressing the button will pass the text to the web service, which will at-
tempt to create a template for that query. If successful the newly created query
will be loaded into the system and all views will be updated accordingly. The
live demo is available at http://ontology.ida.liu.se:8680/iswc/rsp-spin/.
6
http://w3id.org/rsp/spin
Acknowledgments This work was partially supported by the EU FP7 project
Visual Analytics for Sense-making in Criminal Intelligence Analysis (VALCRI)
under grant number FP7-SEC-2013-608142.
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