A model and framework for reliable build systems

Reliable and fast builds are essential for rapid turnaround during development and testing. Popular existing build systems rely on correct manual specification of build dependencies, which can lead to invalid build outputs and nondeterminism. We outline the challenges of developing reliable build systems and explore the design space for their implementation, with a focus on non-distributed, incremental, parallel build systems. We define a general model for resources accessed by build tasks and show its correspondence to the implementation technique of minimum information libraries, APIs that return no information that the application doesn't plan to use. We also summarize preliminary experimental results from several prototype build managers

Perceptions of virtual globes, volunteered geographical information and spatial data infrastructures

The Internet has spawned the development of virtual communities or virtual social networks which generate and share information with one another, and with the public at large. Volunteered geographical information (VGI) refers to user-generated content that is made available as base data on public mapping web sites or as third party data overlaid on virtual globes such as Google Earth and NASA World Wind. Several attempts have been made to determine and categorise what motivates the contributors of VGI. However, while the contributors themselves might generally understand VGI, this is not necessarily the case amongst geographical information professionals at large. We used a questionnaire to explore this by gathering some data on the perceptions held by geographical information professionals of virtual globes, VGI and spatial data infrastructures (SDI). These perceptions are important because they influence how VGI and virtual globes will be used in future in the more formal SDI environments of official mapping agencies and other official custodians of spatial data. The questionnaire was administered at a meeting in Addis Ababa, Ethiopia, in April 2009 and at another in Ekurhuleni, South Africa, in June 2009. The results are reported on here. Some of the results confirm previous research, while others raise questions that warrant further research.http://pubs.cig-acsg.ca/journal/ci

Perceptions of virtual globes, volunteered geographical information and spatial data infrastructures

The Internet has spawned the development of virtual communities or virtual social networks which generate and share information with one another, and with the public at large. Volunteered geographical information (VGI) refers to user-generated content that is made available as base data on public mapping web sites or as third party data overlaid on virtual globes such as Google Earth and NASA World Wind. Several attempts have been made to determine and categorise what motivates the contributors of VGI. However, while the contributors themselves might generally understand VGI, this is not necessarily the case amongst geographical information professionals at large. We used a questionnaire to explore this by gathering some data on the perceptions held by geographical information professionals of virtual globes, VGI and spatial data infrastructures (SDI). These perceptions are important because they influence how VGI and virtual globes will be used in future in the more formal SDI environments of official mapping agencies and other official custodians of spatial data. The questionnaire was administered at a meeting in Addis Ababa, Ethiopia, in April 2009 and at another in Ekurhuleni, South Africa, in June 2009. The results are reported on here. Some of the results confirm previous research, while others raise questions that warrant further research.http://pubs.cig-acsg.ca/journal/ci

Comparative ICE Genomics: Insights into the Evolution of the SXT/R391 Family of ICEs

Integrating and conjugative elements (ICEs) are one of the three principal types of self-transmissible mobile genetic elements in bacteria. ICEs, like plasmids, transfer via conjugation; but unlike plasmids and similar to many phages, these elements integrate into and replicate along with the host chromosome. Members of the SXT/R391 family of ICEs have been isolated from several species of gram-negative bacteria, including Vibrio cholerae, the cause of cholera, where they have been important vectors for disseminating genes conferring resistance to antibiotics. Here we developed a plasmid-based system to capture and isolate SXT/R391 ICEs for sequencing. Comparative analyses of the genomes of 13 SXT/R391 ICEs derived from diverse hosts and locations revealed that they contain 52 perfectly syntenic and nearly identical core genes that serve as a scaffold capable of mobilizing an array of variable DNA. Furthermore, selection pressure to maintain ICE mobility appears to have restricted insertions of variable DNA into intergenic sites that do not interrupt core functions. The variable genes confer diverse element-specific phenotypes, such as resistance to antibiotics. Functional analysis of a set of deletion mutants revealed that less than half of the conserved core genes are required for ICE mobility; the functions of most of the dispensable core genes are unknown. Several lines of evidence suggest that there has been extensive recombination between SXT/R391 ICEs, resulting in re-assortment of their respective variable gene content. Furthermore, our analyses suggest that there may be a network of phylogenetic relationships among sequences found in all types of mobile genetic elements