Database

4-Apr-11 20:50

If your requirement is not to loose data in case of a disaster, have a look at database mirroring, especially synchronous High-safety mode: http://msdn.microsoft.com/en-us/library/ms191456.aspx[^]

The need to optimize rises from a bad design.My articles[^]

Re: Realtime Backups

Mycroft Holmes4-Apr-11 22:21

Mycroft Holmes

4-Apr-11 22:21

This is a standard setup for a high a proficiency site, you need mirroring (as Mika suggested) and more probably failover web and database servers. I would suggest talking to a hosting site, it may be simpler to pay someone else to do these.

Never underestimate the power of human stupidity
RAH

Re: Realtime Backups

Wendelius5-Apr-11 6:03

5-Apr-11 6:03

Good addition Smile | :)

Marked as good answer.

The need to optimize rises from a bad design.My articles[^]

Schema ideas

Super Lloyd4-Apr-11 17:58

Super Lloyd

4-Apr-11 17:58

In our application the user can define custom "user defined type" called "data context" to store a bunch of named datetime/string/number/list(Guid)
such as (for example)
--
Contact Information
Name
Age
Address
Birthday
--
we store that in the DB with some table like that (simplified version)

Sets -- a such item, ex: a contact information
id Guid
idDef Guid -- PK to the type definition table

SetValues -- store the values, ex: Contact.Name
id Guid
idSet Guid -- PK to a record in Sets
idDef Guid -- PK to the type definition table
Value sql_variant

In fact it's a it more complicated (deep) due to list and list with property (2 more tables to store the value of a single user type value)
The problem is it's quite cumbersome to do a search for a value for example and we were thinking to store the data instead, in a table like that

Sets
id Guid
string1 nvarchar(max)
...
string15 nvarchar(max)
datetime1 datetimeoffset(7)
..
datetime15 datetimeoffset(7)
number1 decimal(8,2)
..
number15 decimal(8,2)
list1 uniqueidentifier
..
list15 uniqueidentifier

I'm not sure I explain my problem clearly but.. what I wonder is: is there a clever schema that will allow to store the untyped hierarchical user data, yet makes it easy to join / search, etc...

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
_________________________________________________________
My programs never have bugs, they just develop random features.

Re: Schema ideas

Wendelius4-Apr-11 18:50

4-Apr-11 18:50

Hi,

If I understood you correctly, you have already created tables where you can handle dynamic amount of attributes and values. Querying such tables is often a bit tricky if you have several levels etc, but CTE[^] is a helpful tool when handling dynamic hierarchies.

On the other hand another possibility could be to use XML data type. This would allow you flatten the relational hierarchy and still be able to use highly dynamic values.

The need to optimize rises from a bad design.My articles[^]

Re: Schema ideas

Super Lloyd4-Apr-11 18:56

Super Lloyd

4-Apr-11 18:56

Yeah, XML data type, someone mentioned that... Have to have a look, thanks!! Smile | :)

I though I knew about CTE already but.. didn't know ou can use them for recursive queries!!! mm... thanks (again!)!

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
_________________________________________________________
My programs never have bugs, they just develop random features.

Re: Schema ideas

Wendelius4-Apr-11 19:15

A question about design Relational Model

4-Apr-11 19:15

No problem Smile | :)

The need to optimize rises from a bad design.My articles[^]

Duc Huy Nguyen2-Apr-11 22:31

Duc Huy Nguyen

2-Apr-11 22:31

Hi guys, I've learnt 'bout database designing and I got a difficulty that you can help.
Here the question is: a relation R has 3 attributes, A,B,C and A is a primary key. Then I want to insert new attribute D. In each tuple of R, value of attribute D is assigned by (value of B + value of C).
My task is using Relational algebra, writing a expression to do so.
Below is an example
R - before doing anything
A B C
1 10 9
2 3 7
3 9 6
4 12 0
5 1 5
R - after inserting attribute D
A B C D
1 10 9 19
2 3 7 10
3 9 6 15
4 12 0 12
5 1 5 6

Anyway, thanks alot for reading my question and helping my solve this problem

Wendelius2-Apr-11 22:41

2-Apr-11 22:41

It's not quite clear what your actual question is but concerning calculated columns. It's typically best to avoid columns which are calculations based on the values of the same (or other) rows. This is because you have to take care that when the original values change, also the result of the calculation is changed.

If you're using SQL Server, then things are a bit different since the database has the ability to use computed columns (see: http://msdn.microsoft.com/en-us/library/ms191250.aspx[^]).

If your question is about updating the value, then:
- first insert the new column
- then update the existing rows. Something like:

UPDATE R
SET D = A + B

The need to optimize rises from a bad design.My articles[^]

Eddy Vluggen3-Apr-11 1:50

3-Apr-11 1:50

Duc Huy Nguyen wrote:
My task is using Relational algebra, writing a expression to do so.

That sounds complicated. I'd rephrase that to "you need to add a column to the table, that holds the sum of columns B + C". You'd need to alter the table[^], ending up with something like this;

SQL

BEGIN TRAN
-- prep example data
CREATE TABLE [R]
(
	A INT,
	B INT,
	C INT
)

INSERT INTO [R]
	SELECT 1, 10, 9 UNION ALL
	SELECT 2, 3, 7 UNION ALL
	SELECT 3, 9, 6 UNION ALL
	SELECT 4, 12, 0 UNION ALL
	SELECT 5, 1, 5

-- I want to insert new attribute D. In each tuple of R, value of 
-- attribute D is assigned by (value of B  +  value of C).

ALTER TABLE [R]
	ADD D AS [B] + [C]

-- Proof
SELECT *
  FROM [R]

ROLLBACK

I are Troll Suspicious | :suss:

Keith Barrow3-Apr-11 2:33

Keith Barrow

3-Apr-11 2:33

You shouldn't include calculated columns in your table like this, IIRC it breaks first normal form as the columns are no longer atomic. You should put the calculation into your select statements -or- [better] create a View with the calculated column in it.

Sort of a cross between Lawrence of Arabia and Dilbert.[^]
-Or-
A Dead ringer for Kate Winslett[^]

Eddy Vluggen3-Apr-11 20:45

3-Apr-11 20:45

May I ask how it's no longer atomic? The "new" value (the result from the calculation) is a new atomic fact, even though it's derived from other data - it's not a concatenation of both original columns and you cannot deduce the original values from it.

I are Troll Suspicious | :suss:

Keith Barrow3-Apr-11 22:17

Keith Barrow

3-Apr-11 22:17

Eddy Vluggen wrote:
May I ask how it's no longer atomic?

The calculated column relies on other data, it isn't atomic. The classic examples use concatenation, but it is realy a relies upon relationship.

Sort of a cross between Lawrence of Arabia and Dilbert.[^]
-Or-
A Dead ringer for Kate Winslett[^]

Eddy Vluggen4-Apr-11 0:15

4-Apr-11 0:15

Keith Barrow wrote:
The calculated column relies on other data, it isn't atomic

It relies on other data, that's true, but you cannot decompose the value. It's a new atomic fact, not a composition of other facts. Yes, you can deduce it from other data, but in this case only in one direction (as opposed to a birthdate and an age)

Keith Barrow wrote:
The classic examples use concatenation, but it is realy a relies upon relationship.

Any concatenation of characters would fall under this category. The question is whether the fact that's being described is atomic, not the data.

Whether or not a column is computed (and whether or not the value is stored or recomputed), doesn't matter much for the relational model; that's merely an implementation-detail.

I are Troll Suspicious | :suss:

Keith Barrow4-Apr-11 0:29

Keith Barrow

4-Apr-11 0:29

Hmmmm, I get your point, but I don't undertand how:

"hello " + "world" = "hello world"

Is not a new fact, but:

2 + 5 = 7

is.

Sort of a cross between Lawrence of Arabia and Dilbert.[^]
-Or-
A Dead ringer for Kate Winslett[^]

Eddy Vluggen4-Apr-11 8:27

4-Apr-11 8:27

That's not information, that's data. I can't model data. Your first example may be a single fact, contained in a varchar field. The second might be too, but could just as well be a derived fact. Like having two apples and five banana's equalling seven pieces of fruit. The numbers of fruit in store is a different fact, and it might be fetching totals from an apple-database and a banana-database.

An atomic piece of data is a bit. An atomic piece of information, is dependent on context - the key of the table.

Take a look at your name - under what circumstance would you see the "data" as a single entity of atomic data? Which different parts of your name are used under those circumstances?

I are Troll Suspicious | :suss:

Klaus-Werner Konrad5-Apr-11 7:43

5-Apr-11 7:43

In the relational model, there is is no concept of DEcompose the value !
If a value can be composed from other values, COMPOSE it, or you will denormalize the DB !!!

This is (should be) only allowed, if the normal form takes some time for calculation, and the application is time critical.
If this is the case, you should use INSERT and UPDATE triggers to ensure the data consistence

Eddy Vluggen5-Apr-11 8:05

5-Apr-11 8:05

Klaus-Werner Konrad wrote:
If a value can be composed from other values, COMPOSE it

If the original data can be reconstructed from that resulting data, you'll be able to reverse that process.

Klaus-Werner Konrad wrote:
, or you will denormalize the DB !!!

Not according to the theories of Codd.

Klaus-Werner Konrad wrote:
This is (should be) only allowed, if the normal form takes some time for calculation, and the application is time critical.

1) Allowed by whom? If it's my responsibility, then I'll model as I think is correct - if it were something that could simply be "decided" once and for all, they'd put it in a servicepack and be done with it.
2) Has nothing to do with speed.
3) Whether a column is calculated doesn't say anything about the fact "when" it's going to be calculated.

Klaus-Werner Konrad wrote:
If this is the case, you should use INSERT and UPDATE triggers to ensure the data consistence

That would be modeled as a calculated column in the conceptual model. The physical model might specify your solution, but it may also choose from a whole galaxy of other options. Like not including the column at all, and have the calculation in code.

I are Troll Suspicious | :suss:

Klaus-Werner Konrad5-Apr-11 8:10

5-Apr-11 8:10

Well - I'll take your signature as the truth ...

Klaus-Werner Konrad5-Apr-11 8:32

5-Apr-11 8:32

Eddy Vluggen wrote:
If the original data can be reconstructed from that resulting data, you'll be
able to reverse that process.

Bullshit - you cannot reverse the result of a calculation - nevertheless you can have a calculation of other colums ...

Eddy Vluggen wrote:
Not according to the theories of Codd.

You will at least violate 2NF ...

Eddy Vluggen wrote:
1) Allowed by whom? If it's my responsibility, then I'll model as I think is
correct - if it were something that could simply be "decided" once and
for all, they'd put it in a servicepack and be done with it.

Ok, it's YOUR decision, but HERE we're talking about NORMALIZED databases !!!

Eddy Vluggen wrote:
2) Has nothing to do with speed.

Let's assume it's somethig like SUM( SQRT( PI * DRM) )
Depending on your indices and the sort of query this can be a REALLY time consuming operation, and in such a case a denormalization would be valid (=accepted), but colA +colB isn't such a case, 'cause it's cheap to calc.

Eddy Vluggen wrote:
3) Whether a column is calculated doesn't say anything about the fact "when"
it's going to be calculated.

See my response above

Eddy Vluggen wrote:
That would be modeled as a calculated column in the conceptual model.

The relational model from Codd don't know 'calculated column', as this is AGAINST the model by itself ...

Eddy Vluggen5-Apr-11 9:18

5-Apr-11 9:18

Klaus-Werner Konrad wrote:
bullsh*t - you cannot reverse the result of a calculation - nevertheless you can have a calculation of other colums ...

From mp/h to m/s and back.

Klaus-Werner Konrad wrote:
You will at least violate 2NF ...

Second normal form is about finding the complete key. It doesn't make statements on atomicity of facts.

Klaus-Werner Konrad wrote:
Ok, it's YOUR decision, but HERE we're talking about NORMALIZED databases !!!

I know. Stop shouting.

Klaus-Werner Konrad wrote:
Let's assume it's somethig like SUM( SQRT( PI * DRM) )
Depending on your indices and the sort of query this can be a REALLY time consuming operation, and in such a case a denormalization would be valid (=accepted), but colA +colB isn't such a case, 'cause it's cheap to calc.

Let me repeat that; Normalization has nothing to do with speed. It's about creating a theoretical correct model.
A wise man might decide to optimize by denormalizing when implementing the physical layer.

Klaus-Werner Konrad wrote:
The relational model from Codd don't know 'calculated column', as this is AGAINST the model by itself ...

Name the rule that it breaks.

I are Troll Suspicious | :suss:

Klaus-Werner Konrad13-Apr-11 12:44