Advanced Software Engineering
Software Engineering
Time and Global States in Distributed Systems
Simple Synchronization in Synchronous Systems A process sends its internal clock to a UTC Server t + Ttrans not valid because of network variations instead uses t + (max +min) / 2, being transmission max/min bounds Cristian’s Algorithm Method achieves synchronization if round-trip is sufficiently short compared with the accuracy P1 ask for time to P2 P1 receives [...]
Name Services in Distributed Systems
Names are not the only useful means, descriptive attributes can be used too. A client knowing just a few characteristics needs to be able to find a proper service provider. Pure Names: uninterpreted bit patterns, always need to be lookup. e.g. Object’s address Non-Pure Names: contain information about the location Binding: Association between name and [...]
Definition of Software Development
This definition is from the book “Software as Capital” by Howard Baetjer Jr : Software development is a social learning process. The process is a dialogue in which the knowledge that must become the software is brought together and embodied in the software. The process provides interaction between users and designers: between users and evolving [...]
Distributed File Systems
Requirements of a Distributed File System Transparency: Access Transparency: Programs written to operate local files are able to access remote ones without modification Location Transparency: Uniform name space, files maybe relocated without changing path-names Mobility Transparency: no change of administration tables or client programs when files are moved Performance Transparency: Clients continue to perform satisfactorily [...]
Distributed Objects and Remote Invocation
Properties of middle providing remote invocation and events: Location transparency: Invoking client does know where the receiver is located nor even those objects sending or receiving events. Communication Protocols: UDP/TCP Computer Hardware: They hide properties such byte-ordering Operating Systems: Independent from OSs Programming Languages: CORBA allows interaction between different programming languages Distributed Objects Can be [...]
Group Communication in Distributed Systems
Charateristics: Fault tolerance based on replicated services: Client request multicast to a bunch of server. Finding the discovery servers in spontaneous networking Better performance through replicated data: when a value changes it is multicasted Propagation of event notifications: IP Multicast: Sender is unaware of the identities of the recipients Multicast group is a class D [...]
Interprocess Communication in Distributed Systems
Here some brief notions about CORBA and RMI. CORBA CDR (Common Data Representation) represents all data type used as arguments and return values 15 primitive types such as short, long, unsigned short, unsigned long, float double, char, boolean, octect, etc any represents any basic or construct type. Primitive types: transmitted in sender’s ordering, floating point [...]
Distributed Systems Models
Architectural Models: considers Placement of the component across the Network, to distribute workload and data. Interrelationships between components. Platform: Lowest-level hardware and software layers, including OS till APIs. Middleware: Communication and resource sharing for distributed apps. CORBA: naming, security, transactions, persistent storage and event notification. Fault tolerance: needs to be included in the application, not [...]
Characterization of Distributed Systems
As part of my MSc in Computer Engineering I have to study all over again some introductory books to several subjects. These books are often way too boring for all of us which have been working in the IT world for several years because they are focused mainly to undergraduate students. But I like to think that [...]
Twitter Internal Fragmentation: Python + Twitter
As a toy project to play a little bit more with Python and accessing Twitter, I came out with the idea of calculating the Internal Fragmentation of user’s tweet. To interface with Twitter services I used the Twitter extension located at http://code.google.com/p/python-twitter/, which has a pretty straightforward API. The script shown below gives you back [...]
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