Vipul Pathak

Friday, July 26, 2013

Difference Between Software Architecture And Software Design

I had this question in my mind for years. Based on some experience, some good books (listed in good reads) and my constant interaction with some architecture geniuses at work, I now have clarity on this :-)

Generally speaking, architecture is a branch of design. So every architectural work is a kind of design, but the reverse is not true. Not all design is architecture. Architectural designs addresses a specific goal. The goal almost always is to assure that the system meet its quality attributes and behavioral requirements. The architect creates design that manifest significant decisions and constraints in the system’s architectural structure. There are also design decisions, that are not architecturally significant, i.e. does not belongs to the architecture branch of design. We can view them as some component’s internal design decisions, like- choice of algorithm, selection of data structure etc. Any design decision, which isn’t visible outside of its component boundary is a component’s internal design and is non-architectural. These are the design decisions a system architect would leave on module designer’s discretion or the implementation team. The implementation team is free to design their subsystem as long as their design don’t break the architectural constraints imposed by the system level architecture.

Architecture can be detailed or descriptive, such as defining a protocol that will be used by outside world entities to interact with the system (e.g. A hypermedia RESTful interface for a service of a large system), OR it may be some constraints defined at high level to support quality attributes and to be followed by the system’s internal implementation (e.g. The usage information of all the 6 resources should be collected every 15 seconds and stored in-memory in binary format with memory usage of no more than 16 bits per sample; The usage info buffer should be uploaded to server every 8 hours or whenever the coverage is available after 8 hours).

Architectural design deals with the quality attributes (performance, security, changeability, reliability, user experience etc.) and behavioral requirements (e.g. Usage information of devices should be upload to server with least possible network footprint) of the system/element. Anything that needs design but is not in the above two categories, IS element’s internal design AND NOT system’s architectural design. However, module designers may have to introduce structure or may have to take design decisions to fulfill the behavioral requirements of their module. In that case, those design decisions are architectural to their module, but not to entire system. Hence, design decisions to be called as architectural or not, is a function of the context.

Saturday, July 20, 2013

What is Software Architecture – Some Thoughts

Filed under: Architecture,Technical — Vipul Pathak @ 03:49
Tags: , , , ,

 

Casually speaking, Software architecture is the careful partitioning or subdivision of a system as whole, into sub-parts with specific relationship between these sub-parts. This partitioning is what allows different people (or group(s) of people) to work together cooperatively to solve a much bigger problem, then any of them could solve by individually dealing with it. Each person (or team of persons) creates a software part (you may want to call it a component, module or a sub-system) that interacts with other person’s (or team’s) software part. This interaction happens through carefully crafted interfaces that exposes minimum but most stable information necessary for interaction.

The larger and complex the system is, the more critical is this subdivision. A system is almost always, unavoidably can be divided into parts in more than one way. Each way of division, results in creation of architectural structure. Each way of dividing the system into parts, relationships between them and the way they interact (interface), is a result of careful design to satisfy the driving quality attribute (security, performance, changeability etc.) and business goal behind them. So a system may be sub-divided into parts in different ways, if the driving quality attribute or business goal is different.

Finally, a formal definition of software architecture from IEEE -

“The fundamental organization of a system embodied in its components, their relationships to each other, and to the environment, and the principles guiding its design and evolution.”

Why architecture is important?

Software architecture is a set of design decisions which are hard to revert later and if made incorrectly, may cause the project to cancel or be unsuccessfully. Since these architectural design decisions are the ones that permits a system to meet its quality attributes and behavioral requirements, if these decisions go wrong, the system cannot achieve the desired quality or behavior. The quality attributes are usually parts of requirements (non-functional requirements) and failing to fulfill these requirements automatically invalidate the solution.

Sunday, May 30, 2010

Friday, May 14, 2010

Status Returned By BlackBerry API During "Data Connection Refused" Conditions

The following reading were recorded on 13 BlackBerry mobile phone. Some of them (columns marked with *) were Blackberry phone with correct Blackberry data plan, while some of them were simple non blackberry phones (like- Nokia 6600, explicitly shown) with GPRS connectivity. One of them were even lacking the GPRS connectivity. I studied the data connectivity with an intention to record the behaviour of RIM’s BlackBerry API in low or no data connectivity conditions.

The BlackBerry devices used of the study includes- BlackBerry 9000 (Bold), BlackBerry 8320 (Curve), BlackBerry 8110 (Pearl), BlackBerry 8800, BlackBerry 8300 (Curve) etc. The BlackBerry JDE used was 4.3.

Row number 1 and 2 (Carrier? And MDS?) represents values returned by CoverageInfo.getCoverageStatus().

All “True +ve” shown above are real Data Connection Refused cases. Below is a cut down version of the above table with only the required data. Two of “True +ve” are matching with each other (Column D and E below). However, Column C (being a True +ve) is matching with all the other “False +ve”, e.g. Column B.

Due to identification of Column B as Out of Coverage (though the indicator on home screen shows capital EDGE), the conclusion based on various Blackberry APIs is confusing.

Saturday, May 08, 2010

Setting READ/WRITE Permissions for the ISAPI Extension Hosted on IIS

The script (or the ISAPI Extension) that we are going to deploy and grant additional permissions, will be writing to a File and hence need WRITE permissions as well. Here is how we will do it:

Find out the User Id

IIS’s World Wide Web Publishing Service executes using the Local System account, but it usually impersonates a different account to execute any ISAPI extension. Do the following to discover which User Id is being used by IIS for impersonating and running the extension:

1. Start Internet Information Services Manager from Administrative Tools under Control Panel.

2. Expand the tree on the left side and select the Website under which the ISAPI extension will be deployed.

3. Next, on the right side, under the IIS group, double click on the Authentication icon (see below):

4. In the resulting listing, under the Features View tab, choose Anonymous Authentication and click on the Edit action.

5. The identity selected in the resulting dialog box is used by IIS for impersonating (see below):

If the identity select isn’t shown clearly, but instead the Application Pool Identity is shown as selected, here is how to find which account is used by the Application Pool:

6. From the left pane, select the Website and click on Basic Settings link from the Actions area at the right. The resulting dialog will tell us, which Application Pool is being used by this Website (see below):

7. Click Cancel and dismiss the dialog. Next, from the left pane, select the Application Pools node just above the Sites node. The right pane will show available application pools. Select the Application Pool, that’s being used by our Website.

8. Now click on the Advanced Settings action under the Actions area on the right side (see below):

9. The Identity property shows the account used by the application pool.

Setting the Directory Permission on NTFS

Now that we know, which account is used by IIS for the purpose of impersonation, let’s set WRITE permissions on the correct directory for the User Id used by IIS. Let’s say- we have an ISAPI Extension or a script that creates or updates a file on the local file system. Based on what we know, we need to grant WRITE permission on a folder where our ISAPI Extension will write. Now since, we know the User Id that will be used by IIS for impersonation, let grant write permission to that user, (see below):

Finally, restart IIS. From the command line, use the command IISReset. We are done J.

Installing an ISAPI Extension as a Wildcard Handler

Filed under: Technical,Web — Vipul Pathak @ 13:47
Tags: , , ,

Starting from IIS 6.0, an ISAPI Extension can be added to any Web site or Application, as a wildcard script. By wild card script, I mean an ISAPI extension can be registered with IIS to execute on every incoming request on Web site/Application. All we need to do it register the extension as a wildcard handler. A wildcard handler receives the incoming request, before the actually intended recipient. There may be multiple wildcard handlers registered on the same site or application, which will all be executed in order. The ISAPI Extension, when invoked by IIS, can process the request and pass the request to another handler in chain. Below is how we will register the wildcard script on an application (or website):

IIS 6.0

  1. Start IIS Manager and expand the tree on the left side.
  2. Select any Application/ Website on which you want to install the wildcard handler. Right click and select Properties.
    Application Properties
    Application Properties
  3. In the Application Settings section on Home Directory or Virtual Directory tab, click on the Configuration.
  4. In the Wildcard Application Maps section on the Mappings tab, click the Insert button.
    Specifying a wildcard handler DLL
    Specifying a wildcard handler DLL
  5. Type or Browse the path of our ISAPI Extension DLL and click OK 3 times to go back at work.

IIS 7.0

  1. Start IIS Manager and expand the tree on the left side.
  2. Select any Application/ Website on which you want to install the wildcard handler.
  3. On the right pane, within the features view, double click on the Handler Mappings icon under IIS section (as shown below).
    Mappings Handler Settings in IIS 7.0
    The Handler Mappings Shortcut in IIS 7.0
  4. Once the page containings all the existing mappings opens, locate the link Add Wildcard Script Map… at the right side and click it (as shown below).
    Link to Add a Wildcard Handler Script
    Link to Add a Wildcard Handler Script
  5. In the resulting dialog, specify the path of our ISAPI extension DLL and give it a name (Below):
    Specify the ISAPI Extension DLL
    Specify the ISAPI Extension DLL
  6. We are done  :-)

Thursday, August 20, 2009

Hello World!

Filed under: Uncategorized — Vipul Pathak @ 13:26

Greetings !!

Wikipedia is great source of free knowledge for nearly all of us. Lets start with supporting Wikipedia :
Wikipedia Affiliate Button

There is also a great source of software engineering audio podcasts available, that you can find at: http://www.se-radio.net. If you like the podcast, you may want to support SE-Radio too:
Support Software Engineering Radio

Will meet you soon here, with my first article.

Cheers.

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