Exposing the myth: object-relational impedance mismatch is a wicked problem

Addressing a problem of software integration is a fact of life for those involved in software development. The popularity of both object and relational technologies means that they will inevitably be used together. However, the combination of these two technologies introduces problems. These problems are referred to collectively as the object-relational impedance mismatch. A mismatch is addressed using one or more mapping strategies, typically embodied in a pattern. A strategy is concerned with correspondence between the schema of a relational database and an object-oriented program. Such strategies are employed in mapping tools such as Hibernate and TopLink, and reinforce the received wisdom that the problem of object-relational impedance mismatch has been solved. In this paper, we observe that it is not clear whether each strategy, as one possible solution, addresses the cause or a symptom of a mismatch. We argue that the problem is not tame and easily resolved; rather it is complex and wicked. We introduce a catalogue of problem themes that demonstrate the complex nature of the problem and provide a way both to talk about the problem and to understand its complexity. In the future, as software systems become more complex and more connected, it will be important to learn from past endeavours. Our catalogue of problem themes represents a shift, in thinking about the problem of object-relational impedance mismatch, from issues of implementation towards an analysis of cause and effect. Such a shift has implications for those involved in the design of current and future software architectures. Because we have questioned the received wisdom, we are now in a position to work toward an appropriate solution to the problem of object-relational impedance mismatch

ORM-mallien aikatehokkuusvertailu .NET-alustoilla

Olio-ohjelmoinnin suosion kasvaessa ja relaatiotietokantajärjestelmien käytön ollessa suosiossa, tuli ongelmaksi näiden kahden teknologian yhdistäminen. Olio-ohjelmoinnin ja relaatiotietokantojen välisiä ongelmia kuvataan yleisesti termillä Object-relational impedance mismatch. Näihin ongelmiin kehitettiin ratkaisuksi Object Relational Mapping (ORM) -malleja. ORM-mallit toimivat välitilana relaatiotietokannan ja ohjelmakoodin välillä helpottaen kehitystyötä. ORM-mallit perustoiminnaltaan hoitavat ohjelmakoodin ja relaatiotietokannan välistä yhteyttä, mutta ne sisältävät myös valmista toimintalogiikkaa, joka tuo lisää resurssivaatimuksia ohjelmalle. Tutkimuksessa tehtiin aikatehokkuusvertailu Dapper ja Entity Framework ORM-malleille käyttäen ADO.NET-ohjelmistokehystä perustason vertailukohtana. Tehokkain kolmesta oli ADO.NET, jonka jälkeen tuli Dapper ja kolmanneksi Entity Framework. Eri .NET-ohjelmistokehykset olivat tasaväkisiä, mutta .NET Core osoittautui nopeammaksi

Managing Inheritance Hierarchies in Object/Relational Mapping Tools

We study, in the context of object/relational mapping tools, the problem of describing mappings between inheritance hierarchies and relational schemas. To this end, we introduce a novel mapping model, called M2ORM2+H, and investigate its mapping capabilities. We first show that M2ORM2+H subsumes three well-know basic representation strategies for mapping a hierarchy to relations. We then show that M2ORM2+H also allows expressing further mappings, e.g., where the three basic strategies are applied independently to different parts of a multi-level hierarchy. We describe the semantics of M2ORM2+H in term of how CRUD (i.e., Create, Read, Update, and Delete) operations on objects (in a hierarchy) can be translated into operations over a corresponding relational database. We also investigate correctness conditions

Multivalent Random Walkers:A computational model of superdiffusive transport at the nanoscale

We present a stochastic model and numerical simulation framework for a synthetic nanoscale walker that can be used to transport materials and information at superdiffusive rates in artificial molecular systems. Our \emph{multivalent random walker} model describes the motion of a walker with a rigid, inert body and flexible, enzymatic legs. A leg can bind to and irreversibly modify surface-bound chemical substrate sites arranged as nanoscale tracks. As the legs attach to, modify, and detach from the sites, the walker moves along these tracks. Walkers are symmetrical and the tracks they walk on are unoriented, yet we show that under appropriate kinetic constraints the walkers can transform the chemical free energy in the surface sites into directional motion, and can do ordered work against an external load force. This shows that multivalent random walkers are a new type of molecular motor, useful for directional transport in nanoscale systems. We model the motion of multivalent random walkers as a continuous-time discrete-state Markov process. States in the process correspond to the chemical state of the legs and surface sites, and transitions represent discrete chemical changes of legs binding to, unbinding from, and modifying the surface sites. The Markov property holds because we let the mechanical motion of the body and unattached legs come to equilibrium in between successive chemical steps, thus the transitions depend only on the current chemical state of the surface sites and attached legs. This coarse-grained model of walker motion allows us to use both equilibrium and non-equilibrium Markov chain Monte Carlo simulation techniques. The Metropolis-Hastings algorithm approximates the motion of a walker\u27s body and legs at a mechanical equilibrium, while the kinetic Monte Carlo algorithm simulates the transient chemical dynamics of the walker stepping across the surface sites. Using these numerical techniques, we find that MVRWs move superdiffusively in the direction of unmodified substrate sites when there is a residence time bias between modified and unmodified sites. This superdiffusive motion persists when opposed by external load forces, showing that multivalent random walkers are \emph{molecular motors} that can transform chemical free energy into ordered mechanical work. To produce these results we devised a distributed object-oriented framework for parallel simulation and analysis of the MVRW model. We use an object-relational mapping to persistently maintain all simulation-related objects as tuples in a relational database. We present a new object-relational mapping technique called the \emph{natural entity framework} which disambiguates the semantics of object identity and uniqueness in the relational and object-oriented programming models. Using the natural entity framework we are able to guarantee the uniqueness of mappings between data stored as objects in the relational database and external data stored in non-transactionally-secured HDF5 data files