It was a very interesting seminar due to the fact that software architecture was still something vague for me (i.e. a computer engineering student much interested in software engineering but who has never handle with projects big enough to need a significant effort in making the architecture).

In his seminar, first of all Kruchten tried to give a definition of Software Architecture coming to the following conclusion:

Software architecture encompasses the significant decisions about:

• the organization of a software system,
• the selection of the structural elements and their interfaces by which the system is composed together with their behaviour as specified in the collaboration among those elements,
• the composition of these elements into progressively larger subsystems,
• the architectural syle that guides this organization, these elements and their interfaces, their collaborations, and their composition.

Software architecture is not only concerned with structure and behaviour, but also with usage, functionality, performance, resilience, reuse, comprehensibility, economic and technological constraints and tradeoffs, and aesthetics.

Although this definition of Software Architecture seems to be comprehensive, surely it is not so easy to understand at the first reading. A simpler definition could be the following:

Architecture is about making decision.

Then Kruchten focused on what architects actually do.

The life of a software architect is a long (and sometimes painful) succession of suboptimal decisions made partly in the dark.

Architects should spend their working time in the following manner:

• 50% Architecting (design, validation, prototyping, documenting, etc.)
• 25% Getting input (from user requirement, other architecture, technology)
• 25% Providing Information (communicating architecture, assisting other stakeholders).

The right balance among these activities is very important in order to not fall in typical situations in which architects don’t know anything about existing technology, or don’t communicate their work to designers.

It’s clear that decision is the key word for Software Architecture, therefore Decision Models, Decision Visualizations and Design Decision Capture Mechanisms are the key tools for architects. Refining models, languages and mechanisms concerning decisions is the purpose of Software Engineering Research in this area.

«If you ever admired those colleagues who stayed in office for more than 10 hours day by day, you should consider the fact that after a specific amount of work time bug rates increase dramatically and work results tend to reach lowest levels. Thus, working too hard for a long period of time could even have a negative effect.» Michael Stal

PASSI (a Process for Agent Societies Specification and Implementation) is a step-by-step requirement-to-code methodology for designing and developing multi-agent societies integrating design models and concepts from both OO software engineering and artificial intelligence approaches using the UML notation. The models and phases of PASSI encompass anthropomorphic representation of system requirements, social viewpoint, solution architecture, code production and reuse, and deployment configuration supporting mobility of agents. The design process with PASSI is supported by PTK (PASSI ToolKit) which is composed by an add-in for Rational Rose and a tool for reusing patterns of agents. [The PASSI Design Process]

I have recently followed the PASSI process to develop an Architecture for Context-Dependent Information Systems, as a component of the middleware layer (the layer between the transport and the application layer). JADE has been the framework I used to work with agents.

JADE (Java Agent DEvelopment Framework) is a software framework fully implemented in Java language. It simplifies the implementation of multi-agent systems through a middle-ware that claims to comply with the FIPA specifications and through a set of tools that supports the debugging and deployment phase. The agent platform can be distributed across machines (which not even need to share the same OS) and the configuration can be controlled via a remote GUI. The configuration can be even changed at run-time by moving agents from one machine to another one, as and when required. The only system requirement is the Java Run Time version 1.4 or later. [JADE Homepage]

I must say that I’m impressed with how much the PASSI process can be so powerful in its semplicity. Have a look at the PASSI Home Page to find out how the steps you have to follow are easy to understand and to put in practice. The partition in five models allows designers to look at the multi-agent system in different ways. The models are: System Requirements Model, Agent Society Model, Agent Implementation Model, Code Model, and Deployment Model. For more information have a look at the PASSI lifecycle.

Looking at the documentation, it would seem that PASSI is a waterfall process, but it is not. PASSI is iterative, sequential and top-down, as the authors (M.Cossentino and C.Potts) write in paragraph 2.2 of the research paper about it. There are two kinds of iteration in PASSI. The first one is related to requirement elicitation and involves dependencies among the System Requirements Model, the Agent Society Model and the Agent Implementation Model. The second type of iteration is related to Multi-Agent System Implementation and takes place inside the Agent Implementation Model in the manner shown in figure.

PASSI has been very helpful to me for developing a well-structured agent-based software application. In particular the Deployment Model helped me to get the picture of the software I was on the point to develop. I’ve been run the Deployment Configuration phase (the only one of Deployment Model) during the phases of Agent Implementation Model because I needed to understand how effectively components (placed in different containers) could communicate among themselves. Moreover, since the application I developed implied agent mobility, I needed some deployments diagrams to describe any constraints on migration and mobility, in order to describe the behaviours of module providing mobility.

PASSI is without doubt a good process to follow but the online documentation about iterations and phases overlap is not clear enough. That’s why I have just written this post!

“WEP suffers from two fundamental deficiencies: it was poorly designed and it was poorly implemented. Other than that, it’s fine.”

H. Berghel and J. Uecker. Wireless Infidelity II: Airjacking. Communications of the ACM, Volume 47, Issue 12, pages 15-20, December 2004.

Problems with your italian keyboard? [Solution]

Installing Java? [Solution]

The airport wireless card doesn’t work?! [Solution]

Can’t you see flash animations in your browser? Have a look here!

Ubuntu is a community developed, linux-based operating system that is perfect for laptops, desktops and servers. It contains all the applications you need - a web browser, presentation, document and spreadsheet software, instant messaging and much more. […] What does Ubuntu mean? Ubuntu is an African word meaning ‘Humanity to others’, or ‘I am what I am because of who we all are’. The Ubuntu distribution brings the spirit of Ubuntu to the software world.

Ubuntu is my favourite Linux distro. It’s very easy to install and to use. Moreover it’s Debian-based. I had no problems installing Ubuntu on my iBook G4: it’s enough to download the Desktop Edition for PowerPC based Apple computers and OpenPower/Power5 computers, burn the CD image to CD, and install Ubuntu.
If you want to keep Mac OS X on your system, first you should free some space on your hard drive by removing or resizing existing partitions. Your iBook G4 will dual boot with Mac OS X and Ubuntu Linux automatically.

Now, what if you want to compile a new kernel?

First of all, why to recompile the kernel or compile a new one? For example, you might want to compile a new kernel in order to take advantage of new features available in the last kernel release, or to take advantage of hardware not included in the stock kernel that came with the distribution you installed. Or again to close potential holes from modules or features that you do not ever use, or to tailor the kernel specifically of your computer hardware resulting in a performance boost. Or just because you love to hack the Linux kernel!

Now, how to configure and compile a new kernel?

• First of all, you need to install some packages.
  sudo apt-get install libncurses5-dev kernel-package dpkg-dev
  
• Now, get a new kernel from kernel.org (I used version 2.6.20) and move it to the kernel sources directory:
  sudo mv linux-2.6.20.tar.bz2 /usr/src
  
• Move to the kernel sources directory and unzip the compressed archive. If it’s a bz2 archive, type:
  cd /usr/src
  sudo bunzip2 linux-2.6.20.tar.bz2
  sudo tar -xvvf linux-2.6.20.tar
  
• Copy the whole kernel directory:
  sudo cp -r linux-2.6.20 linux-2.6.20franciov
  (the string “franciov” is just an example…)
• Remove previous symbolic link and make a new symbolic link:
  sudo rm -f linux
  sudo ln -s linux-2.6.20franciov linux
  
• Move to the new kernel’s root:
  cd linux
  
• Optional. Edit the Makefile modifying the EXTRAVERSION flag:
  sudo vim Makefile
  “EXTRAVERSION = franciov”
• Configure the kernel to be compiled. It’s not the easiest thing in the world, because you have to know every details of your machine, and sometimes this is not enough..
  You might try by yourself by typing:
  sudo make menuconfig
  or download my working configuration file (for iBook G4) and type:
  sudo cp config-2.6.20-franciov /usr/src/linux/.config
• Compile the kernel, create an INITial RamDisk image (initrd) and install the kernel image on the system. Using Ubuntu, it’s possible to do all these operations by running just two commands:

  sudo make-kpkg -initrd –revision=ibookg4 kernel-image kernel-headers modules_image
  
  sudo dpkg -i ../linux-image-2.6.20_ibookg4_powerpc.deb

  Now, if everything has gone well, you have got debian packages containing the kernel image and the kernel headers. Moreover your /boot directory has been modified, thus don’t reboot your machine now.[UPDATE-2007-03-19] Make sure that modules have been installed in /lib/modules/’kernel version’ (in this case ‘kernel version’ = 2.6.20+EXTRAVERSION flag). On the contrary, type sudo make modules_install.

  Note that you can obtain the same effect by typing:
  sudo make
  sudo make modules_install
  sudo make install
  and then by using the mkinitramfs or mkinitrd command to generate an initial ramdisk image. You could avoid this, but make sure to compile filesystems you need statically. However I haven’t tried this method on my iBook G4: my advice is to create a debian package, as shown above.

• In your /boot directory there is the new kernel image vmlinux-2.6.20franciov and the new initial ramdisk image initrd.img-2.6.20franciov. Moreover symbolic links vmlinux and initrd has been modified and this has to be fixed before rebooting your system. To list files in /boot:
  ls -la /boot
  You have to edit your bootloader’s configuration file. In this case the bootloader is yaboot and the configuration file is located in /etc/yaboot.conf.
  sudo vim /etc/yaboot.confIt follows an example of configuration:

   ## The default kernel configuration.
  ## You need to fix the kernel image and the initrd image.
  ## My solution is to avoid the use of symbolic links.
  image=/boot/vmlinux-2.6.17-10-powerpc
  label=Linux
  read-only
  initrd=/boot/initrd.img-2.6.17-10-powerpc
  append="quiet splash"
  
  ## Your new kernel configuration.
  ## You need to add the following lines manually,
  ## according to the name of you images.
  image=/boot/vmlinux-2.6.20franciov
  label=franciov-linux
  read-only
  initrd=/boot/initrd.img-2.6.20franciov
  append="quiet splash" 

• Since yaboot.conf is not read at boot time, the MBR needs to be “refreshed” when this is changed. If you do not do this upon rebooting, none of your changes to yaboot.conf will be reflected at startup. Like getting YABOOT the MBR in the first place, you need to run:
  cd /etc
  sudo ybin -v
• You can reboot your iBook G4 now! Keep your fingers crossed and let me know whether I’ve been helpful to you!

Source: Linux Kernel Hacking Free Course, third edition.