Aggregation v.s. Composition (a review on UML)

Aggregation

Aggregation is a kind of association that specifies a whole/part relationship between the aggregate (whole) and component part. This relationship between the aggregate and component is a weak “has a” relationship as the component may survive the aggregate object. The component object may be accessed through other objects without going through the aggregate object. The aggregate object does not take part in the lifecycle of the component object, meaning the component object may outlive the aggregate object. The state of the component object still forms part of the aggregate object.

An example of aggregation is a History-Class object contains zero or more of Student objects. The state of each Student object has an influence on the state of the History-Class object. If the History-Class object is destroyed, the Student objects may continue to exist.

The UML diagram above illustrates the aggregation association line with an open diamond on the aggregate side.

Composition

Composition is a kind of association very similar to aggregation except where the composite object has sole responsibility for the disposition of the component parts. The relationship between the composite and the component is a strong “has a” relationship, as the composite object takes ownership of the component. This means the composite is responsible for the creation and destruction of the component parts. An object may only be part of one composite. If the composite object is destroyed, all the component parts must be destroyed, or the reference and responsibility of the component part must be handed over to another object. Composition enforces encapsulation as the component parts usually are members of the composite object.

An example of composition is a House object contains zero or more Room objects. The state of each Room object has an influence on the House object. If the House object is destroyed, the Room objects will also be destroyed.

The UML diagram above illustrates the composition association line with a solid diamond on the composite side.

Source: http://www.javadesign.info/DesignConcepts/OOConcepts/aggregationcomposition

Creating a Self-Signed SSL Certificate without a mess of makecert.exe (using SSL Diagnostics Tool)

Introduction:

So you have a server and you need to implement SSL to allow secure (https) communication. What choices do you have? You can buy a certificate from certification authority or you can issue a Self-Signed certificate to yourself. The difference is that your browser “knows” it can trust the certificates from the authorities (it has it installed). But when the browser encounters the https connection with a server with the self-signed certificate, the user is presented with a message like this:

Thus, self-signed certificates are OK for test and development web sites, but generally not OK for public websites.
This article will show you the simplest ways to create a Self-Signed SSL Certificate.

Here are your options. (Or just go to the Best Solution )

Solution 1 (quite long, but recommended by Microsoft)
Setting Up SSL Using IIS and Certificate Server

MS recommends that you get the certificate from the certificate server. This means that you have to have an access to Window 2000 or Windows 2003 server with “Certification Services” installed. You use IIS MMC to generate request to this server. Then using browser you submit this request to the server. Then, when somebody at that server approves the request, you will get back a certificate.
See details at http://support.microsoft.com/default.aspx?kbid=299525

Solution 2 (fast, but sometimes could be tricky)
Creating Self-Signed SSL Certificates using makecert.exe

It is a quite simple solution. The only problem is that sometimes it just doesn’t work, and it’s hard to determine what is wrong. The makecert.exe comes with VS.NET. It you don’t have .NET Framework 1.1 installed, the makecert might be outdated. You can download a newer version from http://download.microsoft.com/download/platformsdk/Update/5.131.3617.0/NT45XP/EN-US/makecert.exe
Just replace yourservername with the computer name of your PC and run:

makecert -r -pe -n “CN=yourservername” -b 01/01/2000 -e 01/01/2050 -eku 1.3.6.1.5.5.7.3.1 -ss my -sr localMachine -sky exchange -sp “Microsoft RSA SChannel Cryptographic Provider” -sy 12

Then go to the IIS “Web Site Properties”, “Directory Security”, “Server Certificate…”, “Assign an existing certificate” and select the new certificate from the list.
It works? Fine! No? Go to the Best Solution

Solution 3 (OK for not-technical users)
Download a test certificate from certification authorities
The certificate companies like VeriSign and Thawte issue test certificates, but they expire after 90 days or so, and the process of getting it could be quite tedious.

Solution 4 (The Best and Recommended)
Create a Self-Signed Certificate using SSL Diagnostics Tool

Avoid all this pain with a nice tool from Microsoft: SSL Diagnostics . Download setup.exe (2112 KB) from here: http://www.microsoft.com/downloads/details.aspx?familyid=CABEA1D0-5A10-41BC-83D4-06C814265282&displaylang=en

Install it and run. In the main window of SSL Diagnostics, right-click the Web site level (shown by [W3SVC/<site number>]), and then click Create New Certificate.

That is it. You are done. Don’t forget to explore other capabilities of this nice tool.

Source: http://pranas.net/Tutorials/ssl/SSLDiagnostics.htm

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