VLDB 2026 Research / reviewers in the wild / expert
Dimitris Paparas
dblp:39/9582
· DBLP profile ↗
11ranked-venue papers
0as first author
3since 2021 · last 2025
0009-0004-1253-9086ORCID · corroborated
Domains — the database's venue-derived domains; a paper can count in several
Theory of computation · 7 · 1 since 2021Databases, data management, data science and information retrieval · 2 · 1 since 2021Artificial intelligence and machine learning · 1 · 1 since 2021Applied, interdisciplinary, general and emerging computing · 1
| Year | Publication | Venue | Position |
|---|---|---|---|
| 2025 | Scaling Laws for Downstream Task Performance in Machine TranslationabstractScaling laws provide important insights that can guide the design of large language models (LLMs). Existing work has primarily focused on studying scaling laws for pretraining (upstream) loss. However, in transfer learning settings, in which LLMs are pretrained on an unsupervised dataset and then finetuned on a downstream task, we often also care about the downstream performance. In this work, we study the scaling behavior in a transfer learning setting, where LLMs are finetuned for machine translation tasks. Specifically, we investigate how the choice of the pretraining data and its size affect downstream performance (translation quality) as judged by: downstream cross-entropy and translation quality metrics such as BLEU and COMET scores. Our experiments indicate that the size of the finetuning dataset and the distribution alignment between the pretraining and downstream data significantly influence the scaling behavior. With sufficient alignment, both downstream cross-entropy and translation quality scores improve monotonically with more pretraining data. In such cases, we show that it is possible to predict the downstream translation quality metrics with good accuracy using a log-law. However, there are cases where moderate misalignment causes the downstream translation scores to fluctuate or get worse with more pretraining, whereas downstream cross-entropy monotonically improves. By analyzing these, we provide new practical insights for choosing appropriate pretraining data. Berivan Isik, Natalia Ponomareva 0001, Hussein Hazimeh 0001, Dimitris Paparas, Sergei Vassilvitskii, Oluwasanmi Koyejo |
ICLR | 4 |
| 2022 | On the Complexity of Optimal Lottery Pricing and Randomized Mechanisms for a Unit-Demand BuyerabstractWe study the optimal lottery problem and the optimal mechanism design problem in the setting of a single unit-demand buyer with item values drawn from independent distributions. Optimal solutions to both problems are characterized by a linear program with exponentially many variables. For the menu size complexity of the optimal lottery problem, we present an explicit, simple instance with distributions of support size 2, and show that exponentially many lotteries are required to achieve the optimal revenue. We also show that, when distributions have support size 2 and share the same high value, the simpler scheme of item pricing can achieve the same revenue as the optimal menu of lotteries. The same holds for the case of two items with support size 2 (but not necessarily the same high value). For the computational complexity of the optimal mechanism design problem, we show that unless the polynomial-time hierarchy collapses (more exactly, ${P}^{{NP}}={P}^{{\#P}}$), there is no efficient randomized algorithm to implement an optimal mechanism even when distributions have support size 3. Xi Chen 0001, Ilias Diakonikolas, Anthi Orfanou, Dimitris Paparas, Xiaorui Sun, Mihalis Yannakakis |
SIAM J. Comput. | 4 |
| 2021 | Dataset or Not? A Study on the Veracity of Semantic Markup for Dataset PagesabstractAbstract Semantic markup, such as , allows providers on the Web to describe content using a shared controlled vocabulary. This markup is invaluable in enabling a broad range of applications, from vertical search engines, to rich snippets in search results, to actions on emails, to many others. In this paper, we focus on semantic markup for datasets, specifically in the context of developing a vertical search engine for datasets on the Web, Google’s Dataset Search. Dataset Search relies on to identify pages that describe datasets. While was the core enabling technology for this vertical search, we also discovered that we need to address the following problem: pages from 61% of internet hosts that provide markup do not actually describe datasets. We analyze the veracity of dataset markup for Dataset Search’s Web-scale corpus and categorize pages where this markup is not reliable. We then propose a way to drastically increase the quality of the dataset metadata corpus by developing a deep neural-network classifier that identifies whether or not a page with markup is a dataset page. Our classifier achieves 96.7% recall at the 95% precision point. This level of precision enables Dataset Search to circumvent the noise in semantic markup and to use the metadata to provide high quality results to users. Tarfah Alrashed, Dimitris Paparas, Omar Benjelloun, Ying Sheng 0002, Natasha F. Noy |
ISWC | 2 |
| 2018 | On the Complexity of Simple and Optimal Deterministic Mechanisms for an Additive BuyerabstractWe show that the Revenue-Optimal Deterministic Mechanism Design problem for a single additive buyer is #P-hard, even when the distributions have support size 2 for each item and, more importantly, even when the optimal solution is guaranteed to be of a very simple kind: the seller picks a price for each individual item and a price for the grand bundle of all the items; the buyer can purchase either the grand bundle at its given price or any subset of items at their total individual prices. The following problems are also #P-hard, as immediate corollaries of the proof: 1. determining if individual item pricing is optimal for a given instance, 2. determining if grand bundle pricing is optimal, and 3. computing the optimal (deterministic) revenue. On the positive side, we show that when the distributions are i.i.d. with support size 2, the optimal revenue obtainable by any mechanism, even a randomized one, can be achieved by a simple solution of the above kind (individual item pricing with a discounted price for the grand bundle) and furthermore, it can be computed in polynomial time. The problem can be solved in polynomial time too when the number of items is constant. Xi Chen 0001, George Matikas, Dimitris Paparas, Mihalis Yannakakis |
SODA | 3 |
| 2017 | The Complexity of Non-Monotone MarketsabstractWe introduce the notion of non-monotone utilities, which covers a wide variety of utility functions in economic theory. We then prove that it is PPAD-hard to compute an approximate Arrow-Debreu market equilibrium in markets with linear and non-monotone utilities. Building on this result, we settle the long-standing open problem regarding the computation of an approximate Arrow-Debreu market equilibrium in markets with CES utility functions, by proving that it is PPAD-complete when the Constant Elasticity of Substitution parameter ρ is any constant less than − 1. Xi Chen 0001, Dimitris Paparas, Mihalis Yannakakis |
J. ACM | 2 |
| 2016 | Clustering on k-edge-colored graphs
Eric Angel, Evripidis Bampis, Alexander V. Kononov, Dimitris Paparas, Emmanouil Pountourakis, Vassilis Zissimopoulos |
Discret. Appl. Math. | 4 |
| 2015 | On the Complexity of Optimal Lottery Pricing and Randomized MechanismsabstractWe study the optimal lottery problem and the optimal mechanism design problem in the setting of a single unit-demand buyer with item values drawn from independent distributions. Optimal solutions to both problems are characterized by a linear program with exponentially many variables. For the menu size complexity of the optimal lottery problem, we present an explicit, simple instance with distributions of support size 2, and show that exponentially many lotteries are required to achieve the optimal revenue. We also show that, when distributions have support size 2 and share the same high value, the simpler scheme of item pricing can achieve the same revenue as the optimal menu of lotteries. The same holds for the case of two items with support size 2 (but not necessarily the same high value). For the computational complexity of the optimal mechanism design problem, we show that unless the polynomial-time hierarchy collapses (more exactly, PNP = P#P), there is no universal efficient randomized algorithm to implement an optimal mechanism even when distributions have support size 3. Xi Chen 0001, Ilias Diakonikolas, Anthi Orfanou, Dimitris Paparas, Xiaorui Sun, Mihalis Yannakakis |
FOCS | 4 |
| 2014 | The Complexity of Optimal Multidimensional PricingabstractWe resolve the complexity of revenue-optimal deterministic auctions in the unit-demand single-buyer Bayesian setting, i.e., the optimal item pricing problem, when the buyer's values for the items are independent. We show that the problem of computing a revenue-optimal pricing can be solved in polynomial time for distributions of support size 2 and its decision version is NP-complete for distributions of support size 3. We also show that the problem remains NP-complete for the case of identical distributions. Xi Chen 0001, Ilias Diakonikolas, Dimitris Paparas, Xiaorui Sun, Mihalis Yannakakis |
SODA | 3 |
| 2013 | Clustering on k-Edge-Colored Graphs
Eric Angel, Evripidis Bampis, Alexander V. Kononov, Dimitris Paparas, Emmanouil Pountourakis, Vassilis Zissimopoulos |
MFCS | 4 |
| 2013 | The complexity of non-monotone marketsabstractWe introduce the notion of non-monotone utilities, which covers a wide variety of utility functions in economic theory. We show that it is PPAD-hard to compute an approximate Arrow-Debreu market equilibrium in markets with linear and non-monotone utilities. Building on this result, we settle the long-standing open problem regarding the computation of an approximate Arrow-Debreu market equilibrium in markets with CES utilities, by proving that it is PPAD-complete when the Constant Elasticity of Substitution parameter, ρ, is any constant less than -1. Xi Chen 0001, Dimitris Paparas, Mihalis Yannakakis |
STOC | 2 |
| 2011 | Flexible use of cloud resources through profit maximization and price discriminationabstractModern frameworks, such as Hadoop, combined with abundance of computing resources from the cloud, offer a significant opportunity to address long standing challenges in distributed processing. Infrastructure-as-a-Service clouds reduce the investment cost of renting a large data center while distributed processing frameworks are capable of efficiently harvesting the rented physical resources. Yet, the performance users get out of these resources varies greatly because the cloud hardware is shared by all users. The value for money cloud consumers achieve renders resource sharing policies a key player in both cloud performance and user satisfaction. In this paper, we employ microeconomics to direct the allotment of cloud resources for consumption in highly scalable master-worker virtual infrastructures. Our approach is developed on two premises: the cloud-consumer always has a budget and cloud physical resources are limited. Using our approach, the cloud administration is able to maximize per-user financial profit. We show that there is an equilibrium point at which our method achieves resource sharing proportional to each user's budget. Ultimately, this approach allows us to answer the question of how many resources a consumer should request from the seemingly endless pool provided by the cloud. Konstantinos Tsakalozos, Herald Kllapi, Evangelia A. Sitaridi, Mema Roussopoulos, Dimitris Paparas, Alex Delis |
ICDE | 5 |