The semantic Web does not yet have the complete infrastructure for supporting data interoperability. Most ontology mapping or alignment efforts have focused on concepts, or the class structure of the schema. Comparatively little has been done on instance mapping or predicate (property) mapping . Yet these considerations should reside at the heart of how semantic Web technologies can assist data interoperability.
We began the UMBEL (Upper Mapping and Binding Exchange Layer) vocabulary and ontology as a reference structure for concepts, a means to help match the discussion of topics and things across the Web. As such, UMBEL is part of a fairly robust library of upper ontologies that are meant to provide the grounding references for what information is about. Domains as diverse as biomedicine, banking, oil and gas, municipal governments, retail, marine organisms and the environment — among many others — have effectively leveraged upper ontologies to get diverse datasets and vocabularies to relate to one another. This is much welcomed, to be sure, and a good indicator of how semantic technologies can begin to approach getting data to interoperate.
Here is one way to look at the data interoperability space from a semantic technologies perspective (as initially informed by Pietranik and Nguyen ):
The overall semantics of the structure — indeed, how the structure itself is defined — comes from which ontology languages and vocabularies are used. From an expressiveness standpoint, particularly in conceptual relations or domain schema, there are a variety of standards and specifications from which to choose . We also have pretty good reference ontologies for many domains and what is called the upper levels. We are also starting, through efforts such as Wikipedia (DBpedia and Wikidata), schema.org, Freebase and OKKAM, to get referencable datasets of entities and their attributes, sometimes organized by type.
Reference groundings for properties, on the other hand, have received virtually no attention . SIO, the Semanticscience Integrated Ontology, is one attempt to provide a reference structure for properties in the science domain. The approach is exemplary, but still lacks the scope required of a general grounding vocabulary. QUDT, the Quantities, Units, Dimensions and Data Types Ontologies, provides a standard vocabulary for measurement quantities, but lacks the scope to capture non-quantitative measures for describing things. Both SIO and QUDT should inform and contribute to a still-needed broader treatment of how to describe entities. That is the purpose of the Attributes Ontology in the forthcoming new release of UMBEL.
Attributes within the Semantic Technology Stack
The properties in RDF triples (s – p – o) relate two things, the subject and object, to one another. One pragmatic way to understand properties, which are the predicates or verbs of these triple statements, is that they fall into two broad categories. The first category are the properties between or among different things; they are extrinsic to the subject at hand. These relations stipulate hierarchical relationships (
daughterOf), mereological relationships (
isComponent), role relationships (
isKeyInfluencer) or approximation relationships (
relatesTo). Both subjects and objects are concepts or identifiable things (entities).
However, the second category of properties, attribute properties, has a different nature. Attribute properties — attributes for short — are characteristics of an entity or entity type (class). They describe the entity at hand in the nature of key-value pairs. The key is the attribute, and the value is the literal value or object reference. In broad terms, attributes are the specifics of what is contained in a data record for a given instance. Multiple instances, or records, make up what is known as a dataset.
Attribute properties are intrinsic or descriptive properties. The combination of possible attributes for a given entity constitutes the intensional definition of that object. This use of the term attribute is consistent with its research sense as a descriptive characteristic of an object or its computing sense as being a factor of a given object. In the spirit of this inclusive sense of how attributes describe a given thing, we also include annotations and metadata as part of the attributes category of properties as well. All attribute properties provide a description or characteristic for the entity at hand.
Here are some example key-value pairs about me, the entity Mike Bergman, to illustrate the diversity of how attributes may describe things:
hair : red
college : Pomona College
mood : happy
spouse : Wendy
cat : Snuffles
location : 41°41′18″N 91°35′12″W
dateEntered : 02/16/2015
country : USA
city : Iowa City, IA
occupation : CEO
avocation : flyfishing, cooking
Zen and the Art of Motorcycle Maintenance
species : homo sapiens
sex : male
height : 6’3″
graduateSchool : Duke University
maritalStatus : married
blog : http://mkbergman.com
address : 380 Knowling
fullName : Michael K Bergman
The infoboxes in Wikipedia are another example of such attribute types and values. Note that the values may vary widely as to units or quantities or even links to other things. Also note it really does not matter what order the value pairs are presented and some values refer to other objects (shown as links).
Virtually any data format or data serialization in existence can be expressed in such key-value pairs. Further, related types of entities have related attributes, such that attribute relationships are an alternative way to describe typologies. My attributes, as a human, are quite similar to attributes for other humans, and somewhat close to other mammals. But my attributes are very different than those for a worm or an automobile.
Even simple attributes can pose a challenge for mapping, absent a grounding framework. My name, for example, is Michael Kermit Bergman, which is often provided as Michael Bergman, Mike Bergman, M K Bergman, mkbergman or Michael K Bergman, and the fields that can capture those variants can capture one to four name parts, all called something different. References, rules, semsets (synonyms, jargon and aliases), and coherent organization are needed to ground all of these variants into a common form.
Attribute properties may be quantitative (with a quantitative, measurable value), qualitative, or descriptive or annotative. In many cases, the actual value of an attribute is a literal or numeric value, but it may also be an object, as when the value is a member of an enumerable set or its own defined entity. Describing something as having a color characteristic of red, for example, may result in a literal assignment of the string “red” or it may refer to another object definition where red is specified as to its chromatic properties. Further, if my idea of red was in context with my own personal record (as above), then the referent is more properly something like red hair. Semantics (and, thus, context) matter in data interoperability. I will describe more the rationale and importance of the relation-attribute property split in a following article .
The purpose of semantic technologies is to overcome some 40 categories of semantic heterogeneity, as I most recently discussed in . One interesting aspect is the large number of semantic differences that may be ascribed to attributes, as this table from  shows (see the yellow entries):
|LANGUAGE||Encoding||Ingest Encoding Mismatch||For example, ANSI v UTF-8||Concept|
|Ingest Encoding Lacking||Mis-recognition of tokens because not being parsed with the proper encoding||Concept|
|Query Encoding Mismatch||For example, ANSI v UTF-8 in search||Concept|
|Query Encoding Lacking||Mis-recognition of search tokens because not being parsed with the proper encoding||Concept|
|Languages||Script Mismatch||Variations in how parsers handle, say, stemming, white spaces or hyphens||Concept|
|Parsing / Morphological Analysis Errors (many)||Arabic languages (right-to-left) |
v Romance languages (left-to-right)
|Syntactical Errors (many)||Ambiguous sentence references, such as I’m glad I’m a man, and so is Lola (Lola by Ray Davies and the Kinks)||Concept|
|Semantics Errors (many)||River bank v money bank v billiards bank shot||Concept|
|CONCEPTUAL||Naming||Case Sensitivity||Uppercase v lower case v Camel case||Concept|
|Synonyms||United States v USA v America v Uncle Sam v Great Satan||Concept|
|Acronyms||United States v USA v US||Concept|
|Homonyms||Such as when the same name refers to more than one concept, such as Name referring to a person v Name referring to a book||Concept|
|Generalization / Specialization||When single items in one schema are related to multiple items in another schema, or vice versa. For example, one schema may refer to “phone” but the other schema has multiple elements such as “home phone,” “work phone” and “cell phone”||Concept|
|Aggregation||Intra-aggregation||When the same population is divided differently (such as, Census v Federal regions for states, England v Great Britain v United Kingdom, or full person names v first-middle-last)||Concept|
|Inter-aggregation||May occur when sums or counts are included as set members||Concept|
|Internal Path Discrepancy||Can arise from different source-target retrieval paths in two different schemas (for example, hierarchical structures where the elements are different levels of remove)||Concept|
|Missing Item||Content Discrepancy||Differences in set enumerations or including items or not (say, US territories) in a listing of US states||Concept|
|Missing Content||Differences in scope coverage between two or more datasets for the|
|Attribute List Discrepancy||Differences in attribute completeness between two or more datasets||Attribute|
|Missing Attribute||Differences in scope coverage between two or more datasets for the same attribute||Attribute|
|Item Equivalence||When two types (classes or sets) are asserted as being the same when the scope and reference are not (for example, Berlin the city v Berlin the official city-state)||Concept|
|When two individuals are asserted as being the same when they are actually distinct (for example, John Kennedy the president v John Kennedy the aircraft carrier)||Attribute|
|Type Mismatch||When the same item is characterized by different types, such as a person being typed as an animal |
v human being v person
|Constraint Mismatch||When attributes referring to the same thing have different cardinalities or disjointedness assertions||Attribute|
|DOMAIN||Schematic Discrepancy||Element-value to Element-label Mapping||One of four errors that may occur when attribute names (say, Hair v Fur) may refer to the same attribute, or when same attribute names (say, Hair v Hair) may refer to different attribute scopes (say, Hair v Fur) or where values for these attributes may be the same but refer to different actual attributes or where values may differ but be for the same attribute and putative value.Many of the other semantic heterogeneities herein also contribute to schema discrepancies||Attribute|
|Attribute-value to Element-label Mapping||Attribute|
|Element-value to Attribute-label Mapping||Attribute|
|Attribute-value to Attribute-label Mapping||Attribute|
|Scale or Units||Measurement Type||Differences, say, in the metric |
v English measurement systems, or currencies
|Units||Differences, say, in meters v centimeters v millimeters||Attribute|
|Precision||For example, a value of 4.1 inches in one dataset v 4.106 in another dataset||Attribute|
|Data Representation||Primitive Data Type||Confusion often arises in the use of literals v URIs v object types||Attribute|
|Data Format||Delimiting decimals by period v commas; various date formats; using exponents or aggregate units (such as thousands or millions)||Attribute|
|DATA||Naming||Case Sensitivity||Uppercase v lower case v Camel case||Attribute|
|Synonyms||For example, centimeters v cm||Attribute|
|Acronyms||For example, currency symbols v currency names||Attribute|
|Homonyms||Such as when the same name refers to more than one attribute, such as Name referring to a person v Name referring to a book||Attribute|
|ID Mismatch or Missing ID||URIs can be a particular problem here, due to actual mismatches but also use of name spaces or not and truncated URIs||Attribute|
|Missing Data||A common problem, more acute with closed world approaches than with open world ones||Attribute|
|Element Ordering||Set members can be ordered or unordered, and if ordered, the sequences of individual members or values can differ||Attribute|
We can see that attribute heterogeneities may apply to the attribute itself (the key in a key-value pair), as to what it may contain and what it may refer to, as well as to the actual values and their units and measures. These aspects are important, in that they are the very ones we mean when we talk of data.
Rationale for an Attributes Ontology
When we combine the descriptions of things, we need ways to overcome these sources of semantic heterogeneities. As with concepts, it would be extremely helpful to have a similar attributes vocabulary, and one which is organized according to some logical attribute schema. This combination of vocabulary and schema defines what constitutes an attributes ontology. It can also be a reference grounding for how to relate data from different datasets to one another. Providing this grounding is the driving rationale for UMBEL’s new Attributes Ontology.
In addition to this overarching rationale in data interoperability, a reference Attributes Ontology brings with it a number of benefits:
- More efficient basis for interoperability — the main advantage of a grounding reference is that it allows a spoke-and-hub design for data mapping, which is tremendously more efficient than pairwise mappings. In a spoke-and-hub design, where the reference ontology is the common node at the hub, only n – 1 routes are necessary to connect all sources, meaning that it scales linearly with the number of sources and attributes. Without a grounding reference, these same mapping capabilities would require routes in a pairwise (point-to-point) approach, that also scales poorly as a quadratic function. A system of ten datasets would require 9 composite mappings in the reference grounding case, but 45 in a pairwise approach. And, of course, datasets themselves contain tens to thousands of attributes, compounding the map scaling problem further;
- Higher quality mappings — a single target schema promotes schema enhancements, and toolsets can be justified to automate many processes, leading to;
- Faster integration — these efficiencies lead to faster and more cost-effective mappings;
- Better ability to combine data values across records — which means the approach can be seen as suitable for any content input type (structured, semi-structured or unstructured) or with any form of semantic heterogeneity;
- Faceted browsing and querying — because the nature of the attributes and their values are mapped to a logical schema of attribute relationships, each attribute concept can be the basis of filtering and retrievals, powerfully supporting faceted browsing and querying;
- Infer attribute properties — the logical basis of the attribute schema itself means that relationships and connections may be inferred, and semantics enable different perspectives and language to capture all aspects of the schema. This means the full capabilities of semantic search and querying can be brought to contributing data;
- Highest common denominator — these capabilities mean that source datasets can be lifted and made consistent with a higher standard of testable values and inferences. The rich history of RDFizers points to the usefulness of RDF and related characterizations to bridge between multiple, native data formats . The knowledge of the data already characterized in the system can inform the proper expression of new source data; and
- Better data integration, interoperability — ultimately, of course, all of these factors lead to a complete approach to data interoperability, which leads to being able to finally achieve the objectives of “schema matching” or “data mapping.”
These benefits can be realized in any data integration or interoperability setting. However, the benefits are particularly strong for these use cases:
- Combining records across datasets — the sine qua non of data integration;
- Checking validity of values — having an internal knowledge base of logic, schema, attributes listing and validated values against which to test data updates or new incoming data; and
- Establishing an EIA or MDM capability — creating the internal infrastructure for truly responsive enterprise information integration or master data management. These are the reusable information and knowledge assets that are the grease for any data integration effort. The knowledge bases become assets in and of themselves. The budget sinkholes of most enterprise integration efforts can be turned around to become competitive assets in their own right.
As we have noted many times, these uses also benefit from the incremental and open world ability to expand the scope of the data integration at any point in time .
Description of the Attributes Ontology
We have recognized the importance of the attributes category going back to the first introduction of SuperTypes in UMBEL v.0.80 in 2010 . We noted then that many of the concepts in UMBEL were devoted to how to describe things and the units or quantities associated with their values. We could also see the potential value in having a reference for mapping data characteristics and values.
The first creation of the Attributes SuperType — also introduced in UMBEL v.0.80 in 2010 — aggregated into one place related OpenCyc concepts regarding these descriptors. Working with this category over time surfaced, again, the underlying coherence and use of OpenCyc. We found that UMBEL (via its OpenCyc extraction) already had a strong, logical undergirding to support an organized representation of attributes. Once we understood these patterns, we were able to go back to OpenCyc and better capture other aspects of its attribute structure that we had earlier overlooked. We then added a few aggregate categories to UMBEL to provide a cleaner organization. UMBEL now understands and organizes some 2000 different descriptive attributes.
Over a period of years we did research on exemplars in these areas, with the limited results as first mentioned, notably QUDT and SIO, and also DERA . We also enlisted input from the semantic Web mailing list and were not able to find a suitable extant reference structure . We find it perplexing more work has not been done in this area. We do abhor a vacuum!
Nonetheless, we were able to combine the 2000 attributes infrastructure of OpenCyc into the following upper level of the Attributes Ontology structure:
Note the structure above roughly splits into two parts. The first, AttributeValues, captures the various ways and measures that may be applied to actual values. We foresee a key mapping to QUDT in this part. The second part of the structure, AttributeTypes, organizes the nature of various attributes into similar, logical categories.
We have also added some experimental predicates to the UMBEL vocabulary for mapping domains, ranges and specific external properties to reference attributes. See the ongoing specification in the UMBEL Annex L documentation for other pertinent details.
Though the Attributes Ontology has a bit more structure, it too is a module that segregates out specific attributes into its own files. About 2000 of the UMBEL reference concepts are tagged as attributes; about two-thirds of those, or 1275, are specific attributes that are assigned to the Attributes Ontology, which is also the container for the attributes module.
To our knowledge, the Attributes Ontology (AO) will be the first publicly released attempt to provide an explicit modeling framework for data attributes and values. We expect there to be hiccups and improvements to be made as we work with the system. We expect quite a few release iterations, and experimentation and change. We will retain an experimental designation of the new UMBEL properties and the Attributes Ontology itself until we gain better working comfort with the system.
The Additional UMBEL Entities Module
This new UMBEL Attributes Ontology is being accompanied by the creation of another UMBEL component, the Entities Module. This new module, designed in a similar way to the Geo Module that was released in version 1.05, tags all entities as such and places another 12,000 instances into a separate module. A hierarchy of about 15,000 entity types (and their descriptions and relationships) remain in UMBEL core.
Like the Geo Module, itself comprised of entity instances, the Entities Module may be invoked or not for a given use of UMBEL. The ability to filter on entities and SuperTypes is also a powerful new feature. The fact that there is major disjunction among the SuperTypes also adds to the power of queries and retrievals.
Thus, with the attributes module that is now part of the Attributes Ontology, there are now three separate but invokable modules in addition to the UMBEL core. The Geo, Entities or Attributes modules may be included or not in any given UMBEL deployment.
After five years of sporadically intense thinking, Structured Dynamics is extremely pleased to first formally express our ideas about how to manage and model data and its attributes using the underlying machinery of semantic technologies. We welcome use and commentary on our approach and the Attributes Ontology.
We willl be releasing UMBEL v.1.20 by the end of March with various improvements, including the Entities Module and Attributes Ontology noted above. We are also updating the UMBEL documentation and have added Annexes K and L that describe the Clojure-based UMBEL generation process and the specifics underlying the Attributes Ontology . Shortly thereafter we expect to provide a new minor release that will provide mappings between the UMBEL Attributes Ontology and DBpedia and schema.org properties.
For the time being, we will be focused on refining our use of UMBEL for data interoperability, specifically for attributes. However, we note that the ontology structure used in this article also flags roles and relations as another possible gap. This gap is likely to be the next major focus in UMBEL’s research agenda.