Blogonaut

Go Blue: Went Home to Vote

Go Blue: Went Home to Vote mentions some issues she is having with XSQL1.

I am trying to work through the lecture notes now, and I am stuck at the point where I need to place the file House1XSQL in my XSQL1 directory. I saved the file to my desktop but do not know how to move it to jEdit. Can someone help?

Open up a web browser and an SSH terminal window logged into elab-linux4. In the browser copy the Link Location (Internet Shortcut in IE) for House1XSQL. In the SSH terminal window, navigate to your XSQL1 directory and type wget, hit the spacebar, then paste the link location, and finally hit enter. You will download the House1XSQL.zip file directly into your elab-linux4 space.

Now, unzip that file in your space by typing in your terminal window:

unzip House1XSQL.zip

Now proceed ahead.

Connoisseur: ER Diagram

Connoisseur: ER Diagram poses some questions about cardinality in ER diagrams.

A member of my group said that this left the relationship ambiguous but does this have any implimication as to the nature of their relationship and their effect on the actual database structure?

Basically, you should always express cardinalities in ER diagrams. In ER Exercise 2, we went over how cardinality for ternary relationships is different than for binary relationships, therefore our notation differed.

Cardinality affects database structure in several important ways:

• It determines the placement of foreign keys and not null constraints in one-to-many relationships.
• It determines the creation of additional tables in M:M relationships.
• It can play a role in determining candidate keys for tables implementing M:M relationships.

All of these had examples on the test.

thecrew: Valid Form

thecrew: Valid Form makes some interesting observations about xml including the following:

But in the contrary, i am no so sure whether the data entered into these valid XML must be normalized or not. It seems like a well-formed XML does not have to be normalized to perform the functions required.

I think the analogy between create statements for tables in SQL and DTDs for XML documents is pretty reasonable. We do not have the idea of normalization with XML. Normalization is entirely oriented toward efficient internal storage of data in a database. Note that you can create unnormalized tables in SQL.

maulin: questions about XML

maulin: questions about XML expresses some confusion about XML. In particular, he notes:

Bud mentioned something about how XML is like a standard language now. What was that about? Just want to clarify my understanding about XML.

My advice is to read this link..

icemountain: Sage Question

icemountain: Sage Question asks the following:

Is there a way to view all the blogs from each person? I browsed through the options category, but couldn't find anything. Not a big deal, but just curious.

The feeds produced by typepad only go back 10 posts, and Sage only shows the posts contained in the feed. For most people in the class, that will get you a few weeks of posts. For feed archives of each blogger's posts going back to the beginning of class, look here.

Big Blog in the Sky: Using a laptop in the B-School

Big Blog in the Sky: Using a laptop in the B-School tracked back to me, but he should have linked too.

Mandurro: Laptop Tomorrow?

Mandurro: Laptop Tomorrow? asks:

See I have a wireless card but I've never used it in the B-school, is it really a pain to get it set up to work in the b-school? Or can they do it real quick for you in Kresge?

I think they can do it fast. They have a procedure that I think you can do all yourself.

Hail to the Victors: Exam Results....

Hail to the Victors: Exam Results.... discusses exam misgivings. I had planned to put off my discussion of this till Tuesday, but there is one point she raises that probably merits immediate attention. Here's an interesting point she makes:

It got me thinking though... in real life, how often you come across an ER diagram in isolation with no background explanation attached (such as the examples on the exam)?

There are really two issues here. I'll address the most obvious first which might be rephrased as “Did I just take a test on some meaningless logic interpretations that have no analog in real life?”. You will be lucky to receive complete documentation in many instances when dealing with a database system. A lot of times, you may just get someone's SQL code and be expected to construct the ER diagram or some equivalent. How do the tables relate? The ER diagram seems to be one of the more efficient ways of doing this.

As M Go Blue points out, there is software that will construct the ER diagram for you, but you are still stuck having to interpret ER diagrams. Further, there is no guarantee that you will know a lot about the domain (business context) in question. A lot of times you will just be parachuted in. So, basically the exercise is not meaningless because alot of times, you will feel lucky to have even an ER diagram.

That does not mean that interpreting ER diagrams is easy. In fact, I think it is very hard and have some difficulty with it myself. This leads to the second, more subtle issue I see implicitly buried in Krysta's observation. Basically, we are stuck dealing with logic machines (an observation echoed by Tranquilidad and Kornstein999). SQL, ER diagrams, and normalization are all just part of the same logic machine. They all have the same disconnect with the alogical reality we all experience. To get your projects or any real world endeavor to work right in a database, you will have to understand and deal with this fact.

Big Dog: Realtionships and Tables

Big Dog: Realtionships and Tables refers to one of the many issues raised by bskool bloggin.

Is this always the case with optional relationships in both directions? If so, what is the reasoning behind it?

This is the same logic as for a conditional dependency. Truth be told, it is a minor case.

RissRoss: More on the Exam

RissRoss: More on the Exam asks more exam questions.

1) When using the Like function in Oracle, do you always need to put the wildcard % sign on both sides of the word? or if you only want additional words to be on the left of the word, could you use just one % sign to the left of the word? For example, if you want to find a street name with the last word being Park, would you query as ..... Like %Park? vs. Like%Park%?

Yes, all of these should work as you describe.

2) Where are the attachment links to the rest of the Normalization Exercise #2 questions? I've been meaning to ask - I can not find them.

Not linked on the web page. Sounds like you are in good shape here.

3) When viewing Normalization Problems #2 under the "Employee" Subtitle, question #6, aren't the attributes First Name and Last Name functionally dependent on the SSN of all the people; therefore, wouldn't those attributes fill the transitive dependency definition? If so, how come they were not sorted into a new table when put into 3NF?

No. This is a case where we have two candidate keys SSN and id. We chose id for the primary key, so there is no transitive dependency.