Leveraging Pre-trained Language Models for Time Interval Prediction in Text-Enhanced Temporal Knowledge Graphs

Most knowledge graph completion (KGC) methods learn latent representations of entities and relations of a given graph by mapping them into a vector space. Although the majority of these methods focus on static knowledge graphs, a large number of publicly available KGs contain temporal information stating the time instant/period over which a certain fact has been true. Such graphs are often known as temporal knowledge graphs. Furthermore, knowledge graphs may also contain textual descriptions of entities and relations. Both temporal information and textual descriptions are not taken into account during representation learning by static KGC methods, and only structural information of the graph is leveraged. Recently, some studies have used temporal information to improve link prediction, yet they do not exploit textual descriptions and do not support inductive inference (prediction on entities that have not been seen in training). We propose a novel framework called TEMT that exploits the power of pre-trained language models (PLMs) for text-enhanced temporal knowledge graph completion. The knowledge stored in the parameters of a PLM allows TEMT to produce rich semantic representations of facts and to generalize on previously unseen entities. TEMT leverages textual and temporal information available in a KG, treats them separately, and fuses them to get plausibility scores of facts. Unlike previous approaches, TEMT effectively captures dependencies across different time points and enables predictions on unseen entities. To assess the performance of TEMT, we carried out several experiments including time interval prediction, both in transductive and inductive settings, and triple classification. The experimental results show that TEMT is competitive with the state-of-the-art.Comment: 10 pages, 3 figure

The syntax of Greek polydefinites

The thesis is concerned with the phenomenon of polydefiniteness in Greek. The term polydefinite refers to instances of adjectival modification in which the same definite determiner is multiply realized (to pseftiko to chrisso to roloi 'the fake golden watch'). Polydefinites present free word order variation. It is argued that the construction should be syntactically analyzed on a par with close appositive DPs. Both close appositives and polydefinites are associated with a structure of mutual adjunction, in which the top node inherits non-conflicting properties of both its daughters. The word-order freedom of the construction follows naturally from this proposal, without having recourse to unmotivated syntactic movement. A new interpretive mechanism is proposed, under the name R(eferential)-index mechanism, to capture the semantic effects of the construction (such as the obligatory restrictive reading). I compare my syntactic analysis to LCA-based competitors and argue that my account is superior in a number of respects. Turning to the interpretation of polydefinites, it is argued that the structure assigned to the construction reflects the empirical fact that polydefinites present weak markedness effects. I also discuss the interpretive properties of the R-index mechanism. This proposal allows a natural characterization of the distinction between internal and external modification. This dichotomy is then shown to be instrumental in capturing syntactic and interpretive constraints on determiner spreading. Furthermore, I investigate what happens in Greek indefinites (ena pseftiko chrisso roloi 'a fake golden watch'), which present the same word order variation as polydefinites, but without indefinite determiner spreading. It is shown that analyzing Greek indefinites on a par with Romance indefinites (e.g. French, Spanish) is unwise, because of differences in ordering possibilities and the obligatory restrictiveness associated with Greek post-nominal adjectives. I suggest instead that Greek indefinites with post-nominal adjectives should be analyzed similarly to Greek polydefinites. Following a suggestion in the literature, I argue that the indefinite ena is in fact a quantifier and that the Greek indefinite determiner is phonologically null. On this view, Greek indefinites may exhibit hidden determiner spreading. A tempting correlation that has been suggested in literature is between the Greek polydefinite and the Modern Persian Ezafe constructions. It is explained that these constructions cannot be analyzed similarly to each other due to major syntactic, semantic and configurational differences. They do not constitute therefore, the two sides of the same coin, since their nature is rather different

GEO-ELECTRICAL MAPPING OF BEACHROCK IN VATERA BEACH, LESVOS

Tο Beachrock (Br ή παραλιακοί ψαμμίτες) εμφανίζεται σε παράκτιες ζώνες και έχει σύνθετο ρόλο όσον αφορά στη μορφοδυναμική εξέλιξη τους. Αν και το Br έχει μελετηθεί ευρέως, ωστόσο, δύο βασικά θέματα χρήζουν επιπρόσθετης έρευνας. Το πρώτο αφορά στη σημασία της αλληλεπίδρασης του δυναμικά μεταβαλλόμενου παράκτιου περιβάλλοντος με την χρονικά μεταβαλλόμενη επιφανειακή και υπόγεια υδρογεωλογική ισορροπία. Το δεύτερο θέμα έχει να κάνει με τη χωρική κατανομή και την εξέλιξη του Br σε σχέση με συγκεκριμένο περιβάλλον που το “φιλοξενεί”. H παρούσα εργασία αναδεικνύει τη μέθοδο της ειδικής ηλεκτρικής αντίστασης του υπεδάφους, ως ένα σύγχρονο εργαλείο που μπορεί να συμβάλει στη μελέτη των παραπάνω προβληματισμών. Η έρευνα περιέλαβε μετρήσεις με τη γεωηλεκτρική μέθοδο συνεχούς ρεύματος κατά μήκος δύο τομών στην παραλία των Βατερών της Λέσβου, όπου παρατηρούνται σημαντικές επιφανειακές εμφανίσεις Br. Πραγματοποιήθηκαν δώδεκα γεωηλεκτρικές βυθοσκοπήσεις, με ανάπτυγμα ηλεκτροδίων Axial Pole-Dipole. Οι μετρήσεις της ειδικής ηλεκτρικής αντίστασης επέτρεψαν μία έμμεση εκτίμηση του TDS, το οποίο απεικονίζει την διεπιφάνεια γλυκού-θαλασσινού νερού. Κατά την ερμηνεία του γεωηλεκτρικού μοντέλου αναδείχθηκαν δύο σχηματισμοί που αντιστοιχούν σε Br. Ο πρώτος αποτελεί επέκταση του Br προς την ξηρά και ο δεύτερος πιστεύεται ότι είναι Br σε πρώιμο στάδιο ωρίμανσης.Beachrock (Br) is encountered on the coastal zones, playing an important but also complex role in their morphodynamic evolution. Although Br has been widely studied, two important issues require further investigation. The first concerns the importance of the interaction of the dynamically changing coastal environment with the temporal changing surficial and underground hydrogeological balance. The second has to do with the spatial distribution and the evolution of Br with respect to the specific “host” coastal zone geo environment. This paper designates the electrical resistivity method as a tool that contribute in arguing in the abovementioned issues. The research comprised subsurface measurements with the DC resistivity method along two profiles located on Vatera beach (Lesvos Island), where there is a significant Br outcrops. Twelve geoelectric soundings were carried out using the Axial Pole-Dipole electrode array. The electrical resistively measurements permitted an indirect estimation of TDS, which depicts the coastal interface of fresh water - sea water. The interpreted geoelectric model shows two thin formations attributed to Br. The first is the inland extension of the Br outcrop and the second it is believed to be a primary stage of Br build up

Supporting queries spanning across phases of evolving artifacts using Steiner forests

The problem of managing evolving data has attracted considerable research attention. Researchers have focused on the modeling and querying of schema/instance-level structural changes, such as, ad-dition, deletion and modification of attributes. Databases with such a functionality are known as temporal databases. A limitation of the temporal databases is that they treat changes as independent events, while often the appearance (or elimination) of some structure in the database is the result of an evolution of some existing structure. We claim that maintaining the causal relationship between the two structures is of major importance since it allows additional reason-ing to be performed and answers to be generated for queries that previously had no answers. We present here a novel framework for exploiting the evolution relationships between the structures in the database. In particu-lar, our system combines different structures that are associated through evolution relationships into virtual structures to be used during query answering. The virtual structures define “possible” database instances, in a fashion similar to the possible worlds in the probabilistic databases. The framework includes a query answering mechanism that allows queries to be answered over these possible databases without materializing them. Evaluation of such queries raises many interesting technical challenges, since it requires the discovery of Steiner forests on the evolution graphs. On this prob-lem we have designed and implemented a new dynamic program-ming algorithm with exponential complexity in the size of the input query and polynomial complexity in terms of both the attribute and the evolution data sizes

Discovering Dense Correlated Subgraphs in Dynamic Networks

Given a dynamic network, where edges appear and disappear over time, we are interested in finding sets of edges that have similar temporal behavior and form a dense subgraph. Formally, we define the problem as the enumeration of the maximal subgraphs that satisfy specific density and similarity thresholds. To measure the similarity of the temporal behavior, we use the correlation between the binary time series that represent the activity of the edges. For the density, we study two variants based on the average degree. For these problem variants we enumerate the maximal subgraphs and compute a compact subset of subgraphs that have limited overlap. We propose an approximate algorithm that scales well with the size of the network, while achieving a high accuracy. We evaluate our framework on both real and synthetic datasets. The results of the synthetic data demonstrate the high accuracy of the approximation and show the scalability of the framework.Comment: Full version of the paper included in the proceedings of the PAKDD 2021 conferenc