1 Introduction
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advanced faceted search with support of inverse properties and nested properties;
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automatic detection of property paths that connect the resources that matches the facet selection with those resources that can be shown on the map; and
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a map component that operates directly on a SPARQL endpoint and automatically adopts its data retrieval strategy based on the amount of available spatial information.
2 Rsine - Getting Notified on Linked Data Changes
2.1 Related Work
2.2 Approach
2.2.1 Subscribing for Notifications
2.3 Stack Integration
RepositoryConnectionListenerAdapter
. It intercepts the triple changes and, before handing them down to the triple store for persistence, announces them to rsine’s HTTP interface.2.4 Notification Scenarios
3 CubeViz – Exploration and Visualization of Statistical Linked Data
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The Integrity Analysis Component (cf. Sect. 3.2) evaluates the existence and the quality of selected RDF graphs according to given integrity constraints.
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The Chart Visualization Component (cf. Sect. 3.4) receives all observation as input, that correspond to the given filter conditions, in order to generate a chart visualization.
3.1 The RDF Data Cube Vocabulary
qb:Observation
11, that is used to type all statistical observations being part of a Data Cube. Every observation has to follow a specific structure that is defined using the class qb:DataStructureDefinition
(DSD) and referenced by a dataset resource (DS) of type qb:DataSet
. Since every observation should refer to one specific DS (which again refers to the corresponding DSD) the structure of the observation is fully specified. DSD components are defined as set of dimensions (qb:DimensionProperty
), attributes (qb:AttributeProperty
) and measures (qb:MeasureProperty
) to encode the semantics of observations. Those component properties are used to link the corresponding elements of dimensions, measure values and units with the respective observation resource. Furthermore, it is possible to materialize groups and slices of observations as well as hierarchical orders of dimension elements using respective concepts.3.2 Integrity Analysis
ASK
-clause returning boolean values. The queries were integrated into the Integrity Analysis Component of CubeViz, whose GUI is depicted in Fig. 3. If a query returns false, the corresponding constraint is marked in the GUI in red and can be selected in order to reuse and modify them with a configured query editor. This functionality supports the discovery of potential modelling or conversion flaws.3.3 Faceted Exploration
SUM
, AVG
, MIN
and MAX
. As a consequence, users have to select at least one element of each dimension. Furthermore, if materialized slices are aggregated within the selected DS an optional facet will be generated to offer a selection from the retrieved slices.3.3.1 Generation of Dialogues
3.3.2 Initial Pre-selection
3.4 Chart Visualisation
4 Facete - A Generic Spatial Facetted Browser for RDF
4.1 User Interface
4.2 Concepts
4.2.1 Faceted Search
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A SPARQL concept is a pair comprising a SPARQL graph pattern and a variable thereof. As such, it intentionally describes a set of resources. For instance, the pair ({?s a Person}, ?s) could be used to describe a set of people. SPARQL concepts are a key enabler for indirect faceted search as they can be used to represent virtually any set of resources (within the expressivity of SPARQL), such as the set of facets, the set of child facets, the set of facet values and the set of resources with geometric information.
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Property Steps are used to navigate from a set of resources to a related set of resources by following a specific property. A direction attribute determines whether to follow a property in forward or inverse direction. Hence, a destination SPARQL concept can be obtained from a given origin SPARQL concept and a property step.
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A Property Path is a sequence of property steps.
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Constraint Specifications express constraints via references to property paths. Constraint specifications are internally translated to corresponding SPARQL graph patterns.
4.2.2 Finding Connections between SPARQL Concepts
4.3 Display of Large Amounts of Geometries
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Based on the users constraints on the facets and the geo-link, a corresponding SPARQL concept, named geo-concept, is created. The geo-concept specifies the set of resources to be shown on the map.
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A count of the number of instances matching the geo-concept is requested. If the count is below a configured threshold, all instances are retrieved at once and placed into the root node of the quad tree.
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If this count exceeds the threshold, the extent of the whole map is split recursively into four tiles of equal size. The recursion stops if either a maximum depth is reached, or if the tiles have reached a certain relative size when compared to the map viewport (e.g. when about \(4\times 4\) tiles are visible). For each tile, the geo-concept is then modified to only refer to resources within that tiles’ bounding box. A tile’s resources are only retrieved, if the new count is again below a configured threshold.
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Tiles that still contain too many geometries are rendered as boxes on the map.