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Module: Mapping Analysis

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Mapping Analysis Component

Introduction

The Mapping Analysis Component implements semantic mapping functionalities for the Optique OBDA platform. These functionalities aid in the construction and maintenance of an OBDA specification. Indeed, the specification of the mapping component of an OBDA specification is the most challenging and complex design activity, as it requires to fill the semantic distance between the ontology and the data sources, which can typically be quite large. Moreover, as in the Optique use cases, the number of mapping assertions that constitute the mapping is quite large and extremely difficult to manage manually.
Therefore, tools for supporting the design and analysis of mappings are critical in creating, debugging, and maintaining a mapping specification.

Mapping anomalies

The analysis performed by the Mapping Analysis Component is based on several notions of anomalous mappings in an OBDA specification. In particular, the notions of inconsistent and redundant mappings, defined both in a local and in a global version, along with the notion of syntactically incorrect mappings.
Naturally, local notions refer to single mapping assertions, while global notions are relative to a whole mapping collection, i.e., a set of mapping assertions.

  1. Local mapping inconsistency: the notion of local inconsistency is based on checking the inconsistency of a single mapping assertion with respect to the ontology and to the data source schema. There are two anomalous situations which are identified by this analysis: head inconsistency, for which the query in the head of a mapping assertion certainly has an empty evaluation in every model for the ontology; body inconsistency, for which the query in the body of a mapping assertion has certainly an empty evaluation in every model for the data source schema.
  2. Global mapping inconsistency: the notion of inconsistency for a set of mapping assertions is based on the idea of checking whether the mapping can be activated by the data source without creating contradictions with the ontology. In other words, if a mapping is globally inconsistent, then it is not possible to activate all its mapping assertions without generating an inconsistency of the whole specification.
  3. Local mapping redundancy: for redundancy we consider a standard notion, meaning one that follows naturally from the semantics of an OBDA system. Considering a mapping consisting of a single mapping assertion m, a mapping assertion m’ is locally redundant with respect to m if adding m’ to the mapping produces a specification that is equivalent to the original one.
  4. Global mapping redundancy: the notion of global mapping redundancy extends the local mapping redundancy to the case in which we consider a whole mapping specification, and not just a single mapping assertion.
  5. Syntactic incorrectness: a single mapping assertion must be syntactically correct both with respect to the syntax of the mapping head and the syntax of the mapping body, and with the entire OBDA specification, i.e., the ontology and the data source schema.

Features of the Mapping Analysis Component

The Mapping Analysis Component adds new features to the Information Workbench (IWB) mapping component and also integrates with the already existing mapping editing features of the IWB.
Specifically, integration with mapping editing allows a combination of mapping editing and analysis through automatic execution of syntactic checks on new or edited mapping rules. Instead, the new features provide the mapping component with the following capabilities:

  1. Syntactic, local and global checks (for both inconsistency and redundancy) on any mapping available in the Optique IWB repository.
  2. Explanation of the mapping analysis results. For inconsistency checks, explanations are given in terms of the combination of the set of ontology axioms and membership assertions that together determine the inconsistency. The membership assertions are generated by the Mapping Analysis Component to verify whether all mappings can be activated without generating inconsistencies.
  3. For each membership assertion of the explanations, the mapping analyzer identifies the set of mapping assertions which are either directly or indirectly responsible for the generation of the membership assertion.
  4. Materialization of the results of the mapping analysis in the shared Optique repository in the IWB platform. All mapping analysis results are translated into RDF triples and stored in the repository for future querying. Inc ase of addition, deletion , or modification of one or more mapping assertions in a mapping, the mapping analysis is automatically reset by the system, and all mapping analysis results are deleted from the repository.

How to use the Mapping Analysis Component

To demonstrate how the Mapping Analysis Component works, a data source, ontology, and mapping collection must have been added in Optique.

  1. Click on the Mappings icon in the main menu. This will direct you to the Mappings page, where you will be able to see all available mappings in the Optique repository.
  2. From the Available Mapping Collections table, select one of the available mappings, and click on the Analyze icon from the right-most column.
  3. In the pop-up menu, select the ontology over which to perform the mapping analysis.
  4. Press submit. This will perform the mapping analysis on the chosen mapping.

An overview of the results of the analysis are shown in the Mapping Analysis Results table of the Mapping Analysis Report section.
This table provides, for each analyzed mapping, its name, the ontology and data source over which it was analyzed, whether there are locally inconsistent mapping assertions, whether the mapping is globally inconsistent, and whether the inconsistency explanations have been computed.

If the analysis has identified local or global inconsistencies, click the Get Explanation icon from the Mapping Analysis Results table to produce all possible inconsistency explanations.

Once mapping analysis has been performed and inconsistency explanations have been computed, the details of the mapping analysis can be accessed by clicking on the name of the mapping collection. This brings you to the Mapping Collection page.
From the Analysis Results section of the page, you can see a list of tables showing all the anomalies found by the analysis of the mapping.

1. Global Inconsistency Explanations. The table lists all the explanations for the global inconsistency (there can be more than one).

  1. Click on any explanation. This brings you to the Mapping Inconsistency Explanation page.
  2. The top table shows all the axioms involved in the Explanation. The second table shows the Provenance information of each OWL assertion in the Explanation.
  3. Click on any Provenance Information. This brings you to the Explanation Provenance Information page. Here, you can see the mapping assertions that are directly (top table, Activated mappings), or indirectly (bottom table, Activating mappings), responsible for the assertion that causes the global mapping inconsistency.

2. Syntactically Incorrect Mapping Assertions. The table lists all the syntactically incorrect mapping assertions and provides a detailed message explaining the error.
3. Locally Inconsistent Mapping Assertions. The table lists all the locally inconsistent mapping assertions and provides a detailed message explaining the error.
4. Local Redundancy Results.

  1. The top table shows every pair of mapping assertions for which the assertion in the first column (the subsumed assertion) is redundant with respect to the mapping in the second column (the subsuming assertion).
  2. The bottom table shows, for each locally redundant mapping assertion, a detailed message explaining the redundancy.

5. Global Redundancy Results. The table lists all the globally redundant mapping assertions and provides a detailed message explaining the redundancy.

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