Matchmaking for covariant hierarchies

We describe a model of matchmaking suitable for the implementation of services, rather than their for their discovery and composition. In the model, processing requirements are modelled by client requests and computational resources are software processors that compete for request processing as the covariant implementations of an open service interface. Matchmaking then relies on type analysis to rank processors against requests in support of a wide range of dispatch strategies. We relate the model to the autonomicity of service provision and briefly report on its deployment within a production-level infrastructure for scientic computing

Safer typing of complex API usage through Java generics

When several incompatible implementations of a single API are in use in a Java program, the danger exists that instances from different implementations may inadvertently be mixed, leading to errors. In this paper we show how to use generics to prevent such mixing. The core idea of the approach is to add a type parameter to the interfaces of the API, and tie the classes that make up an implementation to a unique choice of type parameter. In this way methods of the API can only be invoked with arguments that belong to the same implementation. We show that the presence of a type parameter in the interfaces does not violate the principle of interface-based programming: clients can still completely abstract over the choice of implementation. In addition, we demonstrate how code can be reused between different implementations, how implementations can be defined as extensions of other implementations, and how different implementations may be mixed in a controlled and safe manner. To explore the feasibility of the approach, gauge its usability, and identify any issues that may crop up in practical usage, we have refactored a fairly large existing API-based application suite, and we report on the experience gained in the process

Assessment of hydrology, sediment and particulate organic carbon yield in a large agricultural catchment using the SWAT model

The Soil and Water Assessment Tool (SWAT, 2005) was used to simulate discharge and sediment transport at daily time steps within the intensively farmed Save catchment in south-west France (1110 km2). The SWAT model was applied to evaluate catchment hydrology and sediment and associated particulate organic carbon yield using historical flow and meteorological data for a 10-years (January 1999–March 2009). Daily data on sediment (27 months, January 2007–March 2009) and particular organic carbon (15 months, January 2008–March 2009) were used to calibrate the model. Data on management practices (crop rotation, planting date, fertiliser quantity and irrigation) were included in the model during the simulation period of 10 years. Simulated daily discharge, sediment and particulate carbon values matched the observed values satisfactorily. The model predicted that mean annual catchment precipitation for the total study period (726 mm) was partitioned into evapotranspiration (78.3%), percolation/groundwater recharge (14.1%) and abstraction losses (0.5%), yielding 7.1% surface runoff. Simulated mean total water yield for the whole simulation period amounted to 138 mm, comparable to the observed value of 136 mm. Simulated annual sediment yield ranged from 4.3 t km−2 y−1 to 110 t km−2 y−1 (annual mean of 48 t km−2 y−1). Annual yield of particulate organic carbon ranged from 0.1 t km−2 y−1 to 2.8 t km−2 y−1 (annual mean of 1.2 t km−2 y−1). Thus, the highest annual sediment and particulate carbon yield represented 25 times the minimum annual yield. However, the highest annual water yield represented five times the minimum (222 mm and 51 mm, respectively). An empirical correlation between annual water yield and annual sediment and organic carbon yield was developed for this agricultural catchment. Potential source areas of erosion were also identified with the model. The range of the annual contributing erosive zones varied spatially from 0.1 to 6 t ha−1 according to the slope and agricultural practices at the catchment scale