We are witnessing a paradigm shift in machine learning (ML) and artificial intelligence (AI) from a focus primarily on innovating ML models, the model-centric paradigm, to prioritising high-quality, reliable data for AI/ML applications, the data-centric paradigm. This emphasis on data has led to the development of an economy around data, creating data marketplace platforms where data is traded as a commodity. However, trading data involves constraints that reflect the specific needs of users, such as enriching or augmenting their datasets or creating datasets with particular properties. These constraints pose challenges the data management community has already addressed independently of the marketplace platform context. As such, in this thesis, as a first act of research, we integrate approaches and practices from the data management community into the context of an open-source data marketplace platform, following a survey of industry professionals who produce, trade, and purchase data assets.

Aligned with the objectives of the data-centric AI paradigm to create high-quality training datasets, our research is focused on developing automated methods to identify relevant and related features (e.g., columns) that can be augmented to a given dataset. This effort has led to the research and design of feature discovery, which sits at the intersection of dataset discovery by discovering related datasets, data integration by joining datasets, and feature selection by selecting high-predictive features for ML models. We have developed an automated approach for feature discovery that improves upon existing automated data augmentation techniques, improving the effectiveness and efficiency of finding the most relevant features.

However, with the adoption of automatic approaches, we discovered that in moving towards data-centric AI, we risk detaching not only from model-centric but also from user-centric AI. To assess the extent to which users (e.g., data scientists, data engineers, ML engineers) rely on and trust automatic approaches and to determine their feature discovery pipeline, we conducted 19 interviews based on a use-case study. The results revealed that users doubt the automated methods and want to be involved in the process instead. Consequently, we decided to incorporate the users into the feature discovery process and to explore whether their involvement (e.g., by adding domain and business knowledge) improves the quality of the resulting dataset and the feature discovery process.

Thus, we created a human-in-the-loop approach for feature discovery, which was evaluated by conducting interviews with a subset of our initial candidate pool. The results confirmed that a human-in-the-loop method is more approachable for users as it provides control over and insights into the process, as well as the opportunity to inject their knowledge, ensuring that the resulting dataset is relevant for their data tasks.

With this thesis, we make scientific contributions to the field of data management by offering novel insights into users' workflows and designing and developing resources that enhance feature discovery. We hope our contributions will serve as a valuable resource for future work in user-centric and data-centric feature discovery. ... Read more

In recent years, researchers have developed several methods to automate discovering datasets and augmenting features for training Machine Learning (ML) models. Together with feature selection, these efforts have paved the way towards what is termed the feature discovery process. Data scientists and engineers use automated feature discovery over tabular datasets to add new features from different sources and enrich training data. By surveying data practitioners, we have observed that automated feature discovery approaches do not allow data scientists to use their domain knowledge during the feature discovery process. In addition, automated feature discovery methods can leak private features or introduce biased ones.

In this paper, we introduce the first user-driven human-in-the-loop feature discovery method called HILAutoFeat. We demonstrate the capabilities of HILAutoFeat, which effectively combines automated feature discovery with user-driven insights. Our demonstration is centred around two scenarios: (i) an automated feature discovery scenario -- HILAutoFeat acts as a steward in a large data lake where the user is unaware of the quality and relevance of the data, and (ii) a scenario where HILAutoFeat and the user work together -- the user drives the feature discovery process by adding his domain and business knowledge, while HILAutoFeat performs the intensive computations. ... Read more

Multiple works in data management research focus on automating the processes of data augmentation and feature discovery to save users from having to perform these tasks manually. Yet, this automation often leads to a disconnect with the users, as it fails to consider the specific needs and preferences of the actual end-users of data management systems for machine learning. To explore this issue further, we conducted 19 semi-structured, think-aloud use-case studies based on a scenario in which data specialists were tasked with augmenting a base table with additional features to train a machine learning model. In this paper, we share key insights into the practices of feature discovery on tabular data performed by real-world data specialists derived from our user study. Our research uncovered differences between the user assumptions reported in the literature and the actual practices, as well as some areas where literature and real-world practices align. ... Read more

This paper introduces the 4 tutorials that were organized at the International Conference on Distributed and Event-based Systems (DEBS 2024). ... Read more

The increasing need for data trading across businesses nowadays has created a demand for data marketplaces. However, despite the intentions of both data providers and consumers, today’s data marketplaces remain mere data catalogs. We believe that marketplaces of the future require a set of value-added services, such as advanced search and discovery, that have been proposed in the database research community for years, but are not yet put to practice. With this paper, we report on the effort to engineer and develop an open-source modular data market platform to enable both entrepreneurs and researchers to setup and experiment with data marketplaces. To this end, we implemented and extended existing methods for data profiling, dataset search & discovery, and data recommendation. These methods are available as open-source libraries. In this paper we report on how those tools were assembled together to build topio.market, a real-world web platform for trading geospatial data, that is currently in a beta phase. ... Read more

Machine learning (ML) training data is often scattered across disparate collections of datasets, called data silos. This fragmentation poses a major challenge for data-intensive ML applications: integrating and transforming data residing in different sources demand a lot of manual work and computational resources. With data privacy and security constraints, data often cannot leave the premises of data silos, hence model training should proceed in a decentralized manner. In this work, we present a vision of how to bridge the traditional data integration (DI) techniques with the requirements of modern machine learning. We explore the possibilities of utilizing metadata obtained from data integration processes for improving the effectiveness and efficiency of ML models. Towards this direction, we analyze two common use cases over data silos, feature augmentation and federated learning. Bringing data integration and machine learning together, we highlight new research opportunities from the aspects of systems, representations, factorized learning and federated learning. ... Read more

The increasing need for data trading has created a high demand for data marketplaces. These marketplaces require a set of valueadded services, such as advanced search and discovery, that have been proposed in the database research community for years, but are yet to be put to practice. In this paper we propose to demonstrate the Topio Marketplace, an open-source data market platform that facilitates the search, exploration, discovery and augmentation of data assets. To support filtering, searching and discovery of data assets, we developed methods to extract and visualise a variety of metadata, as well as methods to discover related assets and mechanism to augment them. This paper aims at presenting these methods with a real deployment of the Topio marketplace, comprising hundreds of open and proprietary datasets. ... Read more

Machine Learning (ML) applications require high-quality datasets. Automated data augmentation techniques can help increase the richness of training data, thus increasing the ML model accuracy. Existing solutions focus on efficiency and ML model accuracy but do not exploit the richness of dataset relationships. With relational data, the challenge lies in identifying join paths that best augment a feature table to increase the performance of a model. In this paper we propose a two-step, automated data augmentation approach for relational data that involves: (i) enumerating join paths of various lengths given a base table and (ii) ranking the join paths using filter methods for feature selection. We show that our approach can improve prediction accuracy and reduce runtime compared to the baseline approach. ... Read more

Data science workflows often require extracting, preparing and integrating data from multiple data sources. This is a cumbersome and slow process: most of the times, data scientists prepare data in a data processing system or a data lake, and export it as a table, in order for it to be consumed by a Machine Learning (ML) algorithm. Recent advances in the area of factorized ML, allow us to push down certain linear algebra (LA) operators, executing them closer to the data sources. With this work, we revisit classic data integration (DI) systems and see how these fit into modern data lakes that are meant to support LA as a first-class citizen. ... Read more

Capturing relationships among heterogeneous datasets in large data lakes - traditionally termed schema matching - is one of the most challenging problems that corporations and institutions face nowadays. Discovering and integrating datasets heavily relies on the effectiveness of the schema matching methods in use. However, despite the wealth of research, evaluation of schema matching methods is still a daunting task: there is a lack of openly-available datasets with ground truth, reference method implementations, and comprehensible GUIs that would facilitate development of both novel state-of-the-art schema matching techniques and novel data discovery methods.Our recently proposed Valentine is the first system to offer an open-source experiment suite to organize, execute and orchestrate large-scale matching experiments. In this demonstration we present its functionalities and enhancements: i) a scalable system, with a user-centric GUI, that enables the fabrication of datasets and the evaluation of matching methods on schema matching scenarios tailored to the scope of tabular dataset discovery, ii) a scalable holistic matching system that can receive tabular datasets from heterogeneous sources and provide with similarity scores among their columns, in order to facilitate modern procedures in data lakes, such as dataset discovery. ... Read more

Data scientists today search large data lakes to discover and integrate datasets. In order to bring together disparate data sources, dataset discovery methods rely on some form of schema matching: the process of establishing correspondences between datasets. Traditionally, schema matching has been used to find matching pairs of columns between a source and a target schema. However, the use of schema matching in dataset discovery methods differs from its original use. Nowadays schema matching serves as a building block for indicating and ranking inter-dataset relationships. Surprisingly, although a discovery method’s success relies highly on the quality of the underlying matching algorithms, the latest discovery methods employ existing schema matching algorithms in an ad-hoc fashion due to the lack of openly-available datasets with ground truth, reference method implementations, and evaluation metrics. In this paper, we aim to rectify the problem of evaluating the effectiveness and efficiency of schema matching methods for the specific needs of dataset discovery. To this end, we propose Valentine, an extensible open-source experiment suite to execute and organize large-scale automated matching experiments on tabular data. Valentine includes implementations of seminal schema matching methods that we either implemented from scratch (due to absence of open source code) or imported from open repositories. The contributions of Valentine are: i) the definition of four schema matching scenarios as encountered in dataset discovery methods, ii) a principled dataset fabrication process tailored to the scope of dataset discovery methods and iii) the most comprehensive evaluation of schema matching techniques to date, offering insight on the strengths and weaknesses of existing techniques, that can serve as a guide for employing schema matching in future dataset discovery methods. ... Read more

As data is produced at an unprecedented rate, the need and ex- pectation to make it easily available for the end-users is growing. Dataset Discovery has become an important subject in the data management community, as it represents the means of providing the data to the user and fulfilling an information need. Since the end-user is the one that needs the information and knows what type of information to look for, little has been done to involve the user in the discovery process. This PhD project addresses the topic of interactive data discovery, where the user’s interests are modelled through interactions and used as a context for the discovery process. We aim to develop a system that addresses the problem of minimising the trade-off between efficiency and effectiveness, thus providing accurate re- sults in an interactive fashion. The innovative part of the system consists of extracting the user’s interests and data needs through interactions and using them to enrich the data context and provide tailored results to the user. We describe the steps to create models and methods that would be used in designing the prototype and we relate to previous systems and neighbouring communities for optimising the system. ... Read more