Database Queries that Explain their Work

Provenance for database queries or scientific workflows is often motivated as providing explanation, increasing understanding of the underlying data sources and processes used to compute the query, and reproducibility, the capability to recompute the results on different inputs, possibly specialized to a part of the output. Many provenance systems claim to provide such capabilities; however, most lack formal definitions or guarantees of these properties, while others provide formal guarantees only for relatively limited classes of changes. Building on recent work on provenance traces and slicing for functional programming languages, we introduce a detailed tracing model of provenance for multiset-valued Nested Relational Calculus, define trace slicing algorithms that extract subtraces needed to explain or recompute specific parts of the output, and define query slicing and differencing techniques that support explanation. We state and prove correctness properties for these techniques and present a proof-of-concept implementation in Haskell.Comment: PPDP 201

A Formal Account of the Open Provenance Model

On the Web, where resources such as documents and data are published, shared, transformed, and republished, provenance is a crucial piece of metadata that would allow users to place their trust in the resources they access. The Open Provenance Model (OPM) is a community data model for provenance that is designed to facilitate the meaningful interchange of provenance information between systems. Underpinning OPM is a notion of directed graph, where nodes represent data products and processes involved in past computations, and edges represent dependencies between them; it is complemented by graphical inference rules allowing new dependencies to be derived. Until now, however, the OPM model was a purely syntactical endeavor. The present paper extends OPM graphs with an explicit distinction between precise and imprecise edges. Then a formal semantics for the thus enriched OPM graphs is proposed, by viewing OPM graphs as temporal theories on the temporal events represented in the graph. The original OPM inference rules are scrutinized in view of the semantics and found to be sound but incomplete. An extended set of graphical rules is provided and proved to be complete for inference. The paper concludes with applications of the formal semantics to inferencing in OPM graphs, operators on OPM graphs, and a formal notion of refinement among OPM graphs

Putting Lipstick on Pig: Enabling Database-Style Workflow Provenance

Workflow provenance typically assumes that each module is a “black-box”, so that each output depends on all inputs (coarse-grained dependencies). Furthermore, it does not model the internal state of a module, which can change between repeated executions. In practice, however, an output may depend on only a small subset of the inputs (finegrained dependencies) as well as on the internal state of the module. We present a novel provenance framework that marries database-style and workflow-style provenance, by using Pig Latin to expose the functionality of modules, thus capturing internal state and fine-grained dependencies. A critical ingredient in our solution is the use of a novel form of provenance graph that models module invocations and yields a compact representation of fine-grained workflow provenance. It also enables a number of novel graph transformation operations, allowing to choose the desired level of granularity in provenance querying (ZoomIn and ZoomOut), and supporting “what-if” workflow analytic queries. We implemented our approach in the Lipstick system and developed a benchmark in support of a systematic performance evaluation. Our results demonstrate the feasibility of tracking and querying fine-grained workflow provenance

Scientific Workflow Integration For Services Computing

In recent years, significant scientific advances are increasingly achieved through complex scientific processes. As the exponential growth in computing technologies and scientific data, a scientific workflow may comprise a large number of heterogeneous scientific services and applications, provided by different organizations. These services, applications, and their associated data are usually distributed across heterogeneous computing environments. The integration and management of such scientific workflows are pushing the limits of current workflow technology. This dissertation presents an integrated solution to composing, scheduling, executing and developing scientific workflows and scientific workflow management systems. To provide a foundation for workflow composition, scheduling, execution and management, we propose the first reference architecture for scientific workflow management systems. The reference architecture not only provides a high-level organization of subsystems and their interactions in a workflow system, but also provides a basis for comparison between different systems and a guidance for the architectural design of an SWFMS in a specific scientific domain. To integrate heterogeneous services and applications and enable them composed to workflows, we propose a task template model which not only provides an appropriate abstraction of heterogeneous services and applications, but also encapsulates the composition and mapping of shims and functional task components within a task interface. Our proposed task specification language (TSL) not only integrates heterogeneous services and applications into uniform workflow tasks, but also provides a solution to address both TYPE-I and TYPE-II shimming problems in composing scientific workflows. To schedule scientific workflows in emerging services computing environments, we propose two workflow scheduling algorithms, the SHEFT algorithm and the SCPOR algorithm, to prioritize tasks in a workflow, map tasks onto suitable resources and order the execution of tasks on the assigned resources, so that the workflow makespan can be minimized. Our extensive experiments have shown that our proposed algorithms not only outperform other algorithms for large-scale, data-intensive and compute intensive workflows, but also allow the assigned resources elastically change on demand of the size of workflows. To execute workflows on distributed computing environments, we propose a task run model to model the run-time behaviors of tasks. The proposed task run description language (TRDL) enables the execution of task instances constructed from heterogeneous services and applications. We also develop an SOA based task management subsystem to manage all task templates, task instances and task runs for the invocation and execution of various heterogeneous task components. Finally, our developed SOA based workflow management system, the VIEW system, and a VIEW based workflow application system, the FiberFlow system, validate our architectures, models, languages, and algorithms

Querying and managing opm-compliant scientific workflow provenance

Provenance, the metadata that records the derivation history of scientific results, is important in scientific workflows to interpret, validate, and analyze the result of scientific computing. Recently, to promote and facilitate interoperability among heterogeneous provenance systems, the Open Provenance Model (OPM) has been proposed and has played an important role in the community. In this dissertation, to efficiently query and manage OPM-compliant provenance, we first propose a provenance collection framework that collects both prospective provenance, which captures an abstract workflow specification as a recipe for future data derivation and retrospective provenance, which captures past workflow execution and data derivation information. We then propose a relational database-based provenance system, called OPMPROV that stores, reasons, and queries prospective and retrospective provenance, which is OPM-compliant provenance. We finally propose OPQL, an OPM-level provenance query language, that is directly defined over the OPM model. An OPQL query takes an OPM graph as input and produces an OPM graph as output; therefore, OPQL queries are not tightly coupled to the underlying provenance storage strategies. Our provenance store, provenance collection framework, and provenance query language feature the native support of the OPM model