BI review & help

update: Chris Webb and Mosha commented and made it clear that the reason for this error wrap is the NonEmptyCrossJoin function and nothing else. I also checked and I did not find any other function that wraps underlying errors.

This is something you need to be aware of when you're writing MDX. I don't know whether it's a bug or by-design. I'll be happy
to know (please comment if you know something that I don't).
Consider the following MDX:

SELECT
  NonEmptyCrossJoin
  (
    [Customer].[Customer Geography].[State-Province].&[NSW]&[AU].Children
   ,[Employee].[Employee Department].[Department].&[Sales]
  ) ON 0
FROM [Adventure Works];

The query will return with this error: The Set_Count argument of the NonEmptyCrossJoin function is either negative or larger than the number of sets provided. This is quite reasonable because I written the second argument as a member, where (NonEmpty)CrossJoin expects only sets. So, let's upgrade this member to a set:

SELECT
  NonEmptyCrossJoin
  (
    [Customer].[Customer Geography].[State-Province].&[NSW]&[AU].Children
   ,{[Employee].[Employee Department].[Department].&[Sales]}
  ) ON 0
FROM [Adventure Works];

All I did is wrapping the second argument with {} and we have a set. The query will return 19 columns.
Now, for the interesting part. Let's count the members of this CrossJoin before the we fix it:

WITH
  MEMBER [a] AS
    NonEmptyCrossJoin
    (
      [Customer].[Customer Geography].[State-Province].&[NSW]&[AU].Children
     ,[Employee].[Employee Department].[Department].&[Sales]
    ).Count
SELECT
  [a] ON 0
FROM [Adventure Works];

This return... 0.               
Where is the error?
My guess is that the Count function wraps the error. The NonEmptyCrossJoin returns null and the count of members in null is zero. The meaning of this is that if you'll ever forget to wrap the member with {} you'll always get zero and not an error. This can be very dangerous. Just for the check, running this query after the fix:

WITH
  MEMBER [a] AS
    NonEmptyCrossJoin
    (
      [Customer].[Customer Geography].[State-Province].&[NSW]&[AU].Children
     ,{[Employee].[Employee Department].[Department].&[Sales]}
    ).Count
SELECT
  [a] ON 0
FROM [Adventure Works];

will return 19. This been tested with both SSAS 2005 and 2008 (RC0). The examples here are from RC0.

Be careful with your MDX.

I started a long conversation about this subject in the MDSN SSAS forum. I think that it's a question and a principal that every advanced MDX programmer should be familiar with.

It all started with a customer that needed a standard deviation aggregation. I thought that it would be simple because there's a StdDev function in MDX, but it turned out that my customer had major plans for me: He wanted this aggregation to act for every dimension he puts on his axis. This means that the aggregation is not defined over a specific dimension (such as date), but the std-dev is defined over the current dimension in the axis.

The solution for this problem consists of a principle and an answer.

The Principle
Aggregation or a measure that is based on the current user's query is bad. This can and will result two users to see different results using the same measure. This will cause confusion and disinformation. The sacred principle of One Truth will be desecrated. Taken from the thread, in Chris Webb's words:

"I quite often see people wanting to write calculations that behave differently depending on the query that's being run, and I always tell them not to do it. You can hack something but it's almost impossible to get it work properly for every single possible query - MDX just doesn't work like that"

In the end I explained that to the user and he agreed. One more reason for his approval is that std-dev often doesn't really says something about the data. In other words, it isn't informative. "The standard deviation is 0.432. That means that... ???"

The Answer
If you (or the customer) still insists on that crazy measure, the following MDX will work.

I feel like I don't have the right to write about it after so many bits of information were moving in the web about this subject but I would like to add my point of view (or in fact - my point of code). First of all, I must mention some of those who written about this subject before me. Mosha Pasumansky wrote a long post about it in last may. This post contains some ideas of how to come along with this problem, but none of them is perfect. In fact (as always) - there is no perfect solution for this problem. Another important source of knowledge can be found here in the MSDN forums, where Chris Webb, Thomas Pagel and others discussed it. Now, I would like to add my solution. Take it or leave it - your choice.

First of all, create a column in the time dimension that will be the current day indicator. Thanks to the Data Source View or the UDM approach of SSAS 2005 you don't have to change the relational table itself. Just add a named calculation in the DSV with expression that will be 1 for the row of the current day and null or zero for the others. The expression syntax itself depends on the underlying DB so I won't write it here, but it's very simple. Add this column as an attribute (let's call it CurrentDayInd) in the dimension structure and select its AttributeVisible propertiey to false. That's because we don't need such Attribute Hierarchy in our time dimension. After that, create a new User Hierarchy (you can call it Current Day), where the first level in it will be CurrentDayInd and after it place the day (key) attribute.

Now, what we have here? We have a hierarchy (Current Day) with two members - 1 and zero. The 1 member has only one child which is the current day. Link that member to your regular hierarchy (it's called YSQMD at my place) and here you have it. For example, you can use it that way in the MDX script:

Create Set [Last 30 Days] as
LinkMember([Time].[Current Day].[CurrentDayInd].&[1].Children.Item(0),[Time].[YSQMD])
:
LinkMember([Time].[Current Day].[CurrentDayInd].&[1].Children.Item(0),[Time].[YSQMD]).Lag(30);

I think that this solution is good and elegant. First of all, you don't have to use external functions such as Now(). The second pro is that we use the native OLAP mechanism which saves time and makes the queries run faster. Believe me, you'll feel the difference with big cubes. The last thing is that this solution is easy to understand (at least I think so) and it is easy for maintenance. The big con is that you have to process this dimension (and related cubes) every day. I don't think that it's so bad because most of the organizations do make process every day.

 

As many of you already know, installation on Microsoft Excel on the SSAS 2005 server is needed in order to use Excel functions in MDX. That's very helpful because MDX is lack of many important functions such as Round (!). Many organizations don't like it at all, but here's something that may help. In the SSAS 2005 server you don't need to install the whole program, only the .Net programmability support. In the installation, choose to manually pick up which components you wish to install and then choose the .Net programmability Support as seen in the picture:

Notice that this issue will not be fixed in SSAS 2008, so this tip will be relevant for a long time.

My team master Yaron asked me to check some things in the Panorama Dashboards:

1. Can have two hands in one gauge.
2. Can I show two values in the text of every gauge.

Here are the answers. I think that the second answer is a beautiful one. In fact, I really enjoyed while I thought how to do this.

1. This is simple: Just use the Goal hand as the second hand. In the KPI Wizard go to the Define Goal step and choose Custom formula. Enter the measure you want to see in the second hand.

2. This is beautiful: In the KPI Wizard, go to the Finish step and to the Title part. Click on the little blue arrow and click on "Edit MDX...". Then, write this MDX:

[My Dimension].[My Hierarchy].CurrentMember.Name + '\n' +
[Measures].[First Measure].Name + ': ' +
Generate({[My Dimension].[My Hierarchy].CurrentMember},[Measures].[First Measure]) + '\n' +
[Measures].[Second Measure].Name + ': ' +
Generate({[My Dimension].[My Hierarchy].CurrentMember},[Measures].[Second Measure])

Note that:

• This solution may apply to other BI applications, not only to Panorama.
• This way you can show many values and data, not only two values.
• What the Generate function doing there? The '+' operator needs to have two strings in both sides, so writing only the [Measures].[First Measure] or [Measures].[First Measure].Value will return a numeric value which will cause error. The Generate function used this way will return a string. It generates for the set (which contains only our member) the value of the measure (in the second argument of the formula) and as mentioned, returns it as string.
• '\n' will jump to the next line

I never thought of it until one of my users said it. Sorting the KPI can be a very good idea. Instead of always having the same indicators (gauges, traffic lights, etc.) in the same position of the screen, sorting it can make the viewer expect that the most relevant indicator will be placed in the top-left corner of the screen, the second most-relevant will be placed after it, etc.

Sorting the KPI is a very easy thing. Every end user, even with no clue in MDX can do it by following this:

In the Define KPI wizard, go to the "Select Set" step. Copy the current set. For the example, let's say that the current set is [Products].Members and you want to sort it according to the Sales measure in descending order. Click on the advanced button on the right of the set (The button with the "..." on it) and enter the following MDX statement:

Order([Products].Members, [Measures].[Sales], DESC)

If you want to order in ascending order you can replace the DESC with ASC or not to mention it at all.

I had a little challenge back in work and I solved it (in a couple of hours). Here is the description of the problem and its solution:

Let's say that I have a Products dimension, time dimension and a fact table that describes all the faults which occurred in these products. The new requirement is that: Given a product-tree that describes all the parts of every product, I want to know how many faults occurred to every part. The problem is that the fact table points only to the products and the customer wants to know how many faults happened to the parts.

The two solutions I thought about are:

1. The trivial solution: Build a view above the fact table that takes every row and adds a row for each of its product's parts. That way, the fact will contain every fault that happened to every part. The problem with this solution is that the view is very long to compute.

2. The good solution: Build a parent-child dimension out of the parts table which will describe all the parts of every product. Notice that this dimension is not ragged, meaning that one member can have 2 children while another member in the same level can have 10 children. The next step is to add this MDX Script:

Calculate;

Scope([Measures].[Faults],
         Descendants([Products].[Products].[All],
                           1,
                           After));

   This = Ancestor([Products].[Products].CurrentMember,
                         [Products].[Products].[Level 02]);

End Scope;

Scope([Measures].[Faults],
         [Products].[Products].[Level 02].Members);

   This = ([Products].[Products].CurrentMember)
             -
             Sum([Products].[Products].CurrentMember.Children);

End Scope;

Explanation: The first level of the dimension is the [All] member. The second level is the products and the other levels contain the parts. The first block takes all the parts and inherits their amount of faults from their product ancestor. The second block solves the aggregation problem: Let's say that The bike product has 3 children. The bike had 4 faults in our slice of time, so according to the first block of the script every child has 4 faults. Now, the cube makes its aggregation and now the bikes has 16 faults - 4 of its own and more 4 for every of its parts. The second block decreases the sum of the product's children from the products and the result is that the products have their original number of faults.

This post is about Panorama because it is the UI tool I'm working with, but this can be made with every BI UI tool.

My customer wanted to get the effect shown by Analysis Services 2005 when browsing a dimension (see the picture below). He wanted to see some properties of the members shown in the rows, along with the usual measures. Unfortunately, Panorama (and I'm sure that also other tools) does not have this option in the GIU. The solution is this code:

Create Member CurrentCube.[Measures].[MyProperty] as
  iif(IsLeaf([MyDimension].[MyHierarchy].CurrentMember),
     [MyDimension].[MyHierarchy].CurrentMember.Properties("MyProperty"),
     Null)

Note that declaring only the third row will cause that every member that is not a leaf will cause an error, which is something we don't want the viewer to see. If the dimension has properties for members in other levels too, you can adjust this decleration. This member can be declared either in the DataBase's Script (after the CALCULATE expression) or inside the session/query (not recommended in Panorama). Now, all you have to do is to show the dimension's members in the rows and this new measure in the columns (after or before the regular measures), and you'll get what you want.

I won't cover here the topic of Exception handling in MDX, but show you a funny thing that I have never seen in any computer language. Consider this MDX code:

iif (1.0e+40 * 1.0e+40 = (1/0), "Overflowed", "Didn't Overflow")*

On some processors, this code will output "Overflowed". That's because this multiplication will overflow and (1/0) also overflows, so what we have here is two "overflow values" that are equal.

Where on earth have you seen something like this???

---

* Taken from the book "MDX Solutions" second edition, p. 136

While reading the first chapter of the book "MDX Solutions With MS SQL Server Analysis Services 2005 And Hyperion Essbase", I wrote down some important notes, especially for the MDX beginners. Even if you're experienced user, check this out. You may find something useful.

• If you were a code programmer in your past, you can relax: MDX don't care about capitalization.
• Don't even try to skip an axis: It's impossible and it is meaningless. Use the predefined names for the axis, such as: columns, rows, pages, etc.
• You're new to MDX and the whole OLAP gives you a headache? Try to imagine this as a hypercube. It can help you a lot.
• When writing large queries, pay attention to the "readability" of your MDX. Use the Monospace fonts whenever possible.
• Do NOT think of SQL when learning or working with MDX. Although the syntaxes may look alike, these languages are totally different when you get to know them.
• .Members will give you all regular members. .AllMembers will also include calculated members.
• An expression like [Time].Members won't work if the Time dimension has multiple hierarchies.
• The asterisk (*) can replace the CrossJoin function. It may improve readability of the code.
• When using Order() function, you can specify a sorting criteria which is not shown in the result grid.
  

knowing the rules doesn't mean you know how to play.
A great post in the Panorama blog with a riddle in MDX. No knowledge in MDX is required for this riddle, because they teach you what you need to know to solve this riddle.
Have fun. Believe me - you will.

Update: Look at Mosha Pasumansky's blog for another review at this MDX riddle. He claims that the answer in Panorama's Blog is not complete. While I'm new to MDX, I understand that their answer is not 100% complete, but I think it's enought in order to make their point.