Nikolay Yakovets

We investigate temporal-clique subgraph pattern matching, where edges must both form a specific topological sub-structure and temporally overlap within a specified window. This problem has widespread applications across domains including social networks, life sciences, smart cities, and telecommunications. However, existing subgraph matching techniques are inefficient at processing such queries that combine both temporal and structural constraints. We propose a novel approach that effectively leverages both topological and temporal selectivities of the query to significantly improve processing performance. Our solution introduces key innovations across the query processing pipeline, including a specialized multi-way join operator, an optimized query planner, and an accurate cardinality estimator. Through additional optimizations, we further enhance the efficiency of our approach. Extensive experiments demonstrate that our method substantially outperforms state-of-the-art techniques while requiring minimal additional storage overhead.

Geosocial reachability queries (\textsc{RangeReach}) determine whether a given vertex in a geosocial network can reach any spatial vertex within a query region. The state-of-the-art 3DReach method answers such queries by encoding graph reachability through interval labelling and indexing spatial vertices in a 3D R-tree. We present 2DReach, a simpler approach that avoids interval labelling entirely. Like 3DReach, 2DReach collapses strongly connected components (SCCs) into a DAG, but instead of computing interval labels, it directly stores a 2D R-tree per component over all reachable spatial vertices. A query then reduces to a single 2D R-tree lookup. We further propose compressed variants that reduce storage by excluding spatial sinks and sharing R-trees between components with identical reachable sets. Experiments on four real-world datasets show that 2DReach achieves faster index construction than 3DReach, with the compressed variant yielding the smallest index size among all methods. 2DReach delivers competitive or superior query performance with more stable response times across varying query parameters.

Graph database query languages cannot express algorithms like PageRank, forcing costly data wrangling, while existing solutions such as algorithm libraries, vertex-centric APIs, and recursive CTEs lack the necessary combination of expressiveness, performance, and usability. We present GraphAlg: a domain-specific language for graph algorithms that compiles to relational algebra, enabling seamless integration with query processing pipelines. Built on linear algebra foundations, GraphAlg provides intuitive matrix operations that are amenable to aggressive optimization including sparsity analysis, loop-invariant code motion, and in-place aggregation. Our implementation in AvantGraph demonstrates significant code complexity reduction compared to SQL/Python and Pregel while achieving excellent performance on LDBC Graphalytics benchmarks. GraphAlg establishes that graph databases can serve as unified platforms for both queries and analytics.

We study the optimization of navigational graph queries in the form of the Regular Queries, i.e., queries which combine recursive and pattern-matching fragments. Current approaches to their evaluation are not effective in practice. Towards addressing this, we present a number of novel powerful optimization techniques which aim to constrain the intermediate results during query evaluation. We show how these techniques can be planned effectively and executed efficiently towards the first practical evaluation solution for complex navigational queries on real-world workloads. Indeed, our experimental results show several orders of magnitude improvement in query evaluation performance over state-of-the-art techniques on a wide range of queries on diverse datasets.

Knowledge graphs have soared in popularity by supporting different types of applications and domains. In this context, the property graph data model has become an emerging standard in industry and academia. With its widespread use, there is also an increasing interest in investigating constraints for property graph data and their applications in data profiling. Graph Generating Dependencies (GGDs) are a class of property graph data dependencies that can express constraints on topology and properties of nodes and edges of the graph, making them a suitable candidate to expose an overview of the property graph to the user (profile graph data). However, GGDs can be difficult to set manually. To solve this issue, we propose a framework for discovering GGDs automatically from the property graph to profile graph data. Our framework has three main steps: (1) pre-processing, (2) candidate generation, and, (3) GGD extraction. Our results show that the discovered set of GGDs can give an overview of the input graph, including schema-level information between the graph patterns and attributes.

Database systems depend on cardinality estimates for generation of optimal query execution plans. Selecting an appropriate cardinality estimation technique involves navigating trade-offs, including the accuracy of estimates, time required for estimation, and necessary statistics. These trade-offs can lead to different choices based on the dataset and query workload. Unfortunately there is limited support for advising graph database users in exploring these trade-offs and making the right choices for their scenarios. To address this critical gap, we introduce an advisor tool, HomeRun, which analyzes the performance of various cardinality estimation techniques in given usage scenarios. We explain HomeRun's capabilities using the industry-standard LSQB benchmark and synthetic scenarios. HomeRun reveals how minor changes in the dataset can significantly impact the conclusions about the performance of cardinality estimation techniques.

Zeno Cauter, Nikolay Yakovets. Proceedings of the 1st Workshop on Knowledge Graphs and Large Language Models (KaLLM 2024). 2024.

Graph Generating Dependencies (GGDs) informally express constraints between two (possibly different) graph patterns which enforce relationships on both graph's data (via property value constraints) and its structure (via topological constraints). Graph Generating Dependencies (GGDs) can express tuple- and equality-generating dependencies on property graphs, both of which find broad application in graph data management. In this paper, we discuss the reasoning behind GGDs. We propose algorithms to solve the satisfiability, implication, and validation problems for GGDs and analyze their complexity. To demonstrate the practical use of GGDs, we propose an algorithm which finds inconsistencies in data through validation of GGDs. Our experiments show that even though the validation of GGDs has high computational complexity, GGDs can be used to find data inconsistencies in a feasible execution time on both synthetic and real-world data.