(1) Background: Marker-based 3D motion capture systems (MBS) are considered the gold standard in gait analysis. However, they have limitations for which markerless camera-based 3D motion capture ...systems (MCBS) could provide a solution. The aim of this systematic review and meta-analysis is to compare the accuracy, validity, and reliability of MCBS and MBS. (2) Methods: A total of 2047 papers were systematically searched according to PRISMA guidelines on 7 February 2024, in two different databases: Pubmed (1339) and WoS (708). The COSMIN-tool and EBRO guidelines were used to assess risk of bias and level of evidence. (3) Results: After full text screening, 22 papers were included. Spatiotemporal parameters showed overall good to excellent accuracy, validity, and reliability. For kinematic variables, hip and knee showed moderate to excellent agreement between the systems, while for the ankle joint, poor concurrent validity and reliability were measured. The accuracy and concurrent validity of walking speed were considered excellent in all cases, with only a small bias. The meta-analysis of the inter-rater reliability and concurrent validity of walking speed, step time, and step length resulted in a good-to-excellent intraclass correlation coefficient (ICC) (0.81; 0.98). (4) Discussion and conclusions: MCBS are comparable in terms of accuracy, concurrent validity, and reliability to MBS in spatiotemporal parameters. Additionally, kinematic parameters for hip and knee in the sagittal plane are considered most valid and reliable but lack valid and accurate measurement outcomes in transverse and frontal planes. Customization and standardization of methodological procedures are necessary for future research to adequately compare protocols in clinical settings, with more attention to patient populations.
SHACL is a W3C-proposed schema language for expressing structural constraints
on RDF graphs. Recent work on formalizing this language has revealed a striking
relationship to description logics. SHACL ...expressions can use three fundamental
features that are not so common in description logics. These features are
equality tests; disjointness tests; and closure constraints. Moreover, SHACL is
peculiar in allowing only a restricted form of expressions (so-called targets)
on the left-hand side of inclusion constraints.
The goal of this paper is to obtain a clear picture of the impact and
expressiveness of these features and restrictions. We show that each of the
four features is primitive: using the feature, one can express boolean queries
that are not expressible without using the feature. We also show that the
restriction that SHACL imposes on allowed targets is inessential, as long as
closure constraints are not used.
In addition, we show that enriching SHACL with "full" versions of equality
tests, or disjointness tests, results in a strictly more powerful language.
Instance-based provenance is an explanation for a query result in the form of a subinstance of the database. We investigate different desiderata one may want to impose on these subinstances. ...Concretely we consider seven basic postulates for provenance. Six of them relate subinstances to provenance polynomials, three-valued semantics, and Halpern-Pearl causality. Determinism of the provenance mechanism is the seventh basic postulate. Moreover, we consider the postulate of minimality, which can be imposed with respect to any set of basic postulates. Our main technical contribution is an analysis and characterisation of which combinations of postulates are jointly satisfiable. Our main conceptual contribution is an approach to instance-based provenance through three-valued instances, which makes it applicable to first-order logic queries involving negation.
SHACL is a W3C-proposed schema language for expressing structural constraints on RDF graphs. Recent work on formalizing this language has revealed a striking relationship to description logics. SHACL ...expressions can use three fundamental features that are not so common in description logics. These features are equality tests; disjointness tests; and closure constraints. Moreover, SHACL is peculiar in allowing only a restricted form of expressions (so-called targets) on the left-hand side of inclusion constraints. The goal of this paper is to obtain a clear picture of the impact and expressiveness of these features and restrictions. We show that each of the four features is primitive: using the feature, one can express boolean queries that are not expressible without using the feature. We also show that the restriction that SHACL imposes on allowed targets is inessential, as long as closure constraints are not used. In addition, we show that enriching SHACL with "full" versions of equality tests, or disjointness tests, results in a strictly more powerful language.
SHACL: A Description Logic in Disguise Bogaerts, Bart; Jakubowski, Maxime; Van den Bussche, Jan
arXiv (Cornell University),
06/2022
Paper, Journal Article
Open access
SHACL is a W3C-proposed language for expressing structural constraints on RDF graphs. In recent years, SHACL's popularity has risen quickly. This rise in popularity comes with questions related to ...its place in the semantic web, particularly about its relation to OWL (the de facto standard for expressing ontological information on the web) and description logics (which form the formal foundations of OWL). We answer these questions by arguing that SHACL is in fact a description logic. On the one hand, our answer is surprisingly simple, some might even say obvious. But, on the hand, our answer is also controversial. By resolving this issue once and for all, we establish the field of description logics as the solid formal foundations of SHACL.
In constraint languages for RDF graphs, such as ShEx and SHACL, constraints on nodes and their properties in RDF graphs are known as "shapes". Schemas in these languages list the various shapes that ...certain targeted nodes must satisfy for the graph to conform to the schema. Using SHACL, we propose in this paper a novel use of shapes, by which a set of shapes is used to extract a subgraph from an RDF graph, the so-called shape fragment. Our proposed mechanism fits in the framework of Linked Data Fragments. In this paper, (i) we define our extraction mechanism formally, building on recently proposed SHACL formalizations; (ii) we establish correctness properties, which relate shape fragments to notions of provenance for database queries; (iii) we compare shape fragments with SPARQL queries; (iv) we discuss implementation options; and (v) we present initial experiments demonstrating that shape fragments are a feasible new idea.
