About Star Schema

In a star design, Does each level of the dimension get a row in the dimension table
Eg. Consider City->Start Hierarchy with the following rows
Geog Key City_Key City State_KEY State
1 1 MA 11 Mass
2 2 NYC 12 NY
after all the cities does the table also get rows for the states?
i.e
200 Nul Null 11 MA
Or is this really an application-specifc question ?
Thanks
GR

The levels are actually columns in a star schema.

Similar Messages

  • Star schema in Physical Layer

    Recently, i came across a question from one of colleague. The discussion went as follows:
    He asked me what is star schema and where can you define it? Physical layer or BMM layer?
    I explained about star schema and answered his rest of the doubt that, we define it in BMM layer.
    His immediate question is why can't we define it in Physical layer? Since BMM layer allows to build dimensional models, so, we have to build it in that layer itself is my reply. But, later in the evening, when i started thinking on my way to home, i started thinking about his doubt.
    Here, what am curious to know is since we can join tables in Physical layer too, why can't we define star in Physical layer? and why only in BMM? and what are the difference in the Joins that we made in Physical layer to that of BMM layer?
    I tired getting answers for these in documents and in some other online resources, but, am not succeed. So, am approaching this forum in anticipation. Can anyof you help us understanding these concepts better.

    In OBIEE Server Administration Guide it is written for logical fk join:
    Logical foreign key joins might be needed if the Oracle BI Server is to be used as an ODBC data
    source for certain third-party query and reporting tools. Typically, you should not create logical
    foreign keys. This capability is in the Administration Tool to provide compatibility with previous
    releases.
    And logical complex join:
    The use of logical complex joins is recommended over logical key and foreign key joins.
    And physical complex join:
    In the physical layer of the repository, complex joins are joins over nonforeign key and primary key
    columns. When you create a complex join in the physical layer, you can specify expressions and the
    specific columns on which to create the join. When you create a complex join in the business model
    layer, you do not specify expressions.
    I agree, that always are some special cases, but in general it should be clear when to use which joins.
    So, you should read chapters 4,5 one more time this administration guide [OBIEE server administration guide|http://download.oracle.com/docs/cd/E10415_01/doc/bi.1013/b31770.pdf]

  • Using two facts of two different star schemas and conformed dimensions

    Hi,
    I've been working as developer and database designer for years and I'm new to Business Objects. Some people says you can not use two facts of two different star schemas in the same query because of conformed dimensions and loop problems in BO.
    For example I have a CUSTOMER_SALE_fACT table containing customer_id and date_id as FK, and some other business metrics about sales. And there is another fact table CUSTOMER_CAMPAIGN_FACT which also contains customer_id and date_id as FK, and some  other business metrics about customer campaigns. SO I have two stars like below:
    DIM_TIME -- SALE_FACT -- DIM_CUSTOMER
    DIM_TIME -- CAMPAIGN_FACT -- DIM_CUSTOMER
    Business metrics are loaded into fact tables and facts can be used together along conformed dimensions . This is one of the fundamentals of the dimensional modeling. Is it really impossible to use SALE_FACT and CAMPAIGN_FACT together? If the answer is No, what is the solution?
    Saying "you cannot do that because of loops" is very interesting.
    Thank you..

    When you join two facts together with a common dimension you have created what is called a "chasm trap" which leads to invalid results because of the way SQL is processed. The query rows are first retrieved and then aggregated. Since sales fact and campaign fact have no direct relationship, the rows coming from either side can end up as a product join.
    Suppose a customer has 3 sales fact rows and 2 campaign fact rows. The result set will have six rows before any aggregation is performed. That would mean that sales measures are doubled and campaign measures are tripled.
    You can report on them together, using multiple SQL passes, but you can't query them together. Does that distinction make sense?

  • Injecting data into a star schema from a flat staging table

    I'm trying to work out a best approach for getting data from a very flat staging table and then loading it into a star schema - I take a row from a table with for example 50 different attributes about a person and then load these into a host of different tables, including linking tables.
    One of the attibutes in the staging table will be an instruction to either insert the person and their new data, or update a person and some component of their data or maybe even to terminate a persons records.
    I plan to use PL/SQL but I'm not sure on the best approach.
    The staging table data will be loaded every 10 minutes and will contain about 300 updates.
    I'm not sure if I should just select the staging records into a cursor then insert into the various tables?
    Has anyone got any working examples based on a similar experience?
    I can provide a working example if required.

    The database has some elements that make SQL a tad harder to use?
    For example:
    CREATE TABLE staging
    (person_id NUMBER(10) NOT NULL ,
    title VARCHAR2(15) NULL ,
    initials VARCHAR2(5) NULL ,
    forename VARCHAR2(30) NULL ,
    middle_name VARCHAR2(30) NULL ,
    surname VARCHAR2(50) NULL,
    dial_number VARCHAR2(30) NULL,
    Is_Contactable     CHAR(1) NULL);
    INSERT INTO staging
    (person_id, title, initials, forename, middle_name, surname, dial_number)
    VALUES ('12345', 'Mr', 'NULL', 'Joe', NULL, 'Bloggs', '0117512345','Y')
    CREATE TABLE person
    (person_id NUMBER(10) NOT NULL ,
    title VARCHAR2(15) NULL ,
    initials VARCHAR2(5) NULL ,
    forename VARCHAR2(30) NULL ,
    middle_name VARCHAR2(30) NULL ,
    surname VARCHAR2(50) NULL);
    CREATE UNIQUE INDEX XPKPerson ON Person
    (Person_ID ASC);
    ALTER TABLE Person
    ADD CONSTRAINT XPKPerson PRIMARY KEY (Person_ID);
    CREATE TABLE person_comm
    (person_id NUMBER(10) NOT NULL ,
    comm_type_id NUMBER(10) NOT NULL ,
    comm_id NUMBER(10) NOT NULL );
    CREATE UNIQUE INDEX XPKPerson_Comm ON Person_Comm
    (Person_ID ASC,Comm_Type_ID ASC,Comm_ID ASC);
    ALTER TABLE Person_Comm
    ADD CONSTRAINT XPKPerson_Comm PRIMARY KEY (Person_ID,Comm_Type_ID,Comm_ID);
    CREATE TABLE person_comm_preference
    (person_id NUMBER(10) NOT NULL ,
    comm_type_id NUMBER(10) NOT NULL
    Is_Contactable     CHAR(1) NULL);
    CREATE UNIQUE INDEX XPKPerson_Comm_Preference ON Person_Comm_Preference
    (Person_ID ASC,Comm_Type_ID ASC);
    ALTER TABLE Person_Comm_Preference
    ADD CONSTRAINT XPKPerson_Comm_Preference PRIMARY KEY (Person_ID,Comm_Type_ID);
    CREATE TABLE comm_type
    comm_type_id NUMBER(10) NOT NULL ,
    NAME VARCHAR2(25) NULL ,
    description VARCHAR2(100) NULL ,
    comm_table_name VARCHAR2(50) NULL);
    CREATE UNIQUE INDEX XPKComm_Type ON Comm_Type
    (Comm_Type_ID ASC);
    ALTER TABLE Comm_Type
    ADD CONSTRAINT XPKComm_Type PRIMARY KEY (Comm_Type_ID);
    insert into comm_type (comm_type_id, NAME, description, comm_table_name) values ('23456','HOME PHONE','Home Phone Number','PHONE');
    CREATE TABLE phone
    (phone_id NUMBER(10) NOT NULL ,
    dial_number VARCHAR2(30) NULL);
    Take the record from Staging then update:
    'person'
    'Person_Comm_Preference' Based on a comm_type of 'HOME_PHONE'
    'person_comm' Derived from 'Person' and 'Person_Comm_Preference'
    Then update 'Phone' with the number based on a link derived from 'Phone' which is made up of Person_Comm Primary_Key where 'Comm_ID' (part of that composite key)
    relates to the Phone table Primary_Key which is Phone_ID.
    Does you head hurt as much as mine?

  • Star schema without a fact table?

    Hi,
    I'm preparing my warehouse for using with Discoverer and my question is about the star schema.
    - Is a star schema directly associated with data warehouse?
    - Can I talk about a star schema if a) I do not have a fact table (no summarized values) and b) if I do not have a dimension of time?
    The problem is, I'm thinking of usine Discoverer but should I use it if it's not connected to a data warehouse?
    As I told, I'd like to modelized my data "like" a star schema but my "center table" will contain only the foreign key of my dimensions; no time dimensions, no aggregate data in the center table (fact table).
    Is there another word for the model I'd like to do?
    Thank in advance.

    Hi,
    Is a star schema directly associated with data warehouse?Not really, a star schema is just one where there is one large fact table joined to many smaller dimension tables using key fields. You usually see this in data warehouses.
    Can I talk about a star schema if a) I do not have a fact table (no summarized values) and b) if I do not have a dimension of time?A star schema must have a fact table but it doesn't need contain summarised values or a time dimension.
    You can use Discoverer with any Oracle database, it doesn't have to be a data warehouse.
    Rod West

  • Star schema question

    Hi,
    I have a question about the realization of the star schema. I have familiarized me with the basic concepts of dimensions and fact tables. But what I don’t get is how I “combine” the dimensions with the fact table. I know that the fact table includes the dimension-IDs and measures. But do I use the joiner-operator in the OWB to join the dimension-ID (IDs of the dims are the criteria for the joiner condition) to create the fact table?
    So my understanding is when I have for example 3 dimensions (product dimension, sales dimension, time dimension) and one fact table.
    The realization looks like this:
    product dim ->
    sales dim -> joiner operator = fact table with the IDs of the dims and measure
    time dim ->
    Please correct me if I am wrong.
    If there is something that I can read to this subject of matter it would be very nice if someone could post it.
    Thx

    Hi,
    first you load the dimensions. Every entry has an id (surrogate key) and some business key (coming from the data source).
    When you load the fact, you use the business key from the data source to join (using a joiner or lookup operator) the dimension and get the id (surrogate key) from it. You only load the id and the measures into the fact table.
    Make sure to handle the case that the business key is null or no entry in the dimension can be found.
    If you query the fact table you must always join the dimensions.
    Regards,
    Carsten.

  • Star Schema tables Creation

    If I am creating a BI analytical application from sample Sales Hisotory schema's transactional data, what is the first Step I need to do? Should I create a star schema from the transactional tables? If this is correct, What I tool I need to use to create such tables with data? I believe once this is done I can create dimensions , measures and cubes using OWM11g. Some on please help me. I am very very new to OLAP , But has lots of interest in it
    Thanks
    George

    Hi George,
    If you are working with 11g - did you install all the latest patches? I strongly recommend applying all available patches when working with 11g. All the information you need is here - http://www.oracle.com/technology/products/bi/olap/collateral/olap_certification.html
    As for your question about the criteria for desgining dimension tables, the best advice I can offer is to work with star or snowflake dimensions. You can also see sample schema designs for both at these links
    Also, in case you haven't already seen it, there is a good blog posting on working with different kinds of dimensions/hierarchies here - http://oracleolap.blogspot.com/2008/01/olap-workshop-4-managing-different.html
    Finally, you might find this [white paper|http://www.oracle.com/technology/products/warehouse/pdf/Benefits%20of%20a%20multi-dimensional%20model.pdf] useful as you say you are new to OLAP
    Let me know how you get on
    Thanks,
    Stuart Bunby
    OLAP Blog: http://oracleOLAP.blogspot.com
    OLAP Wiki: http://wiki.oracle.com/page/Oracle+OLAP+Option
    OLAP on OTN: http://www.oracle.com/technology/products/bi/olap/index.html
    DW on OTN : http://www.oracle.com/technology/products/bi/db/11g/index.html

  • No query rewriting in a star schema

    Gentlemen,
    I am facing a problem with query rewriting in a simple data warehouse star schema. I want to take advantage of the built-in roll up along dimensions of a star schema. Therefore, I created several DIMENSIONs and made sure that all foreign key/primary key relationships between fact and dimension tables are set up correctly. In addition, as many table attributes as possible are assigned the NOT NULL constraint, especially the ones that are used by the CHILD Of and ATTRIBUTE relationships.
    I defined materialized views on the fact table and a couple of dimension tables to report on aggregated data. All the MVIEWs are enabled for query rewriting and I have the initialization parameter set correctly (QUERY_REWRITE_INTEGRITY is set to TRUSTED).
    From my tests I learned that a query is rewritten correctly only of the corresponding MVIEW contains the fact table and one dimension table. This is true for every dimension I created. However, as soon as the MVIEW joins more than one dimension table to the fact table the rewriting mechanism fails. It appears that the roll-up (aggregation along the hierarchy) is only possible for one of the dimensions. If the original query suggests rolling-up more than one dimension (e.g., "summarize the key figures by year and product category" but the underlying dimension is based on month and product), the MVIEW is no longer rewritten at all.
    Do you know this effect from your work experience? Is this a bug or have I made a mistake or forgotten to switch on a special feature?
    Here are some technical data of our data warehouse: we are running an Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 on a Windows Server 2003, the size of the database is about 10 GB (excluding indexes), the star schema contains ten dimension tables each one with a simple or parallel hierarchies (e.g. a product dimension). The fact table and the MVIEWS are partitioned by month.
    Any help is very welcome.
    Regards,
    John

    Hi,
    you may ask with DBMS_MVIEW why your query does not get rewritten:
    Maybe you have to create a util table first with
    SQL> @?/rdbms/admin/utlxrw.sql
    Then you ask:
    SQL> begin
    DBMS_MVIEW.EXPLAIN_REWRITE('<your query without ; at the end>');
    end;
    The reason why it is not rewritten:
    SQL> select message from rewrite_table order by sequence;
    Kind regards
    Uwe

  • Converting 3 tables to a star schema ??

    Hi i was trying to prepare a very small demo for an OLAP system. Anyways I have a simple transaction database for a supposed Book Store anyways the database has the following 3 tables :
    Table No:1
    Table Name:Main Table
    This Table contains the following columns:
    Customer Name (PK) | Book Purchase ID (PK) | PRICE
    Table No:2
    Table Name:Customer Table
    This Table contains the following columns:
    Customer Name | CELL | ADDRESS
    Table No:3
    Table Name:BOOKS Table
    This Table contains the following columns:
    BOOK Name | Book Purchase ID | GENRE
    so the above is my transactional database.. LEt me know if i am missing any other detail. Anyways now i want to convert the above to start schema ?? How would i acccomplish that .. I tried to read a couple of tutorials but i was a bit confused... so if you guys could assist me on this i would be really thnakfull.

    David_Aldridge wrote:
    thinking in general about this, it sounds like what you need is a set of four tables:
    Dim_Cust -- stores customer details as a dimension
    Dim_Book -- stores book details as a dimension
    Dim_Date -- stores dates for transactions
    Fct_Book_Sales -- stores the transactions themselves as the purchase of a book for a certain price by a customer on a date.
    Use synthetic keys for all but the Dim_Date.Okay i kind of got lost on the way here is wht i know so far regarding the star schema
    "A star schema consists of fact tables and dimension tables. Fact tables contain the quantitative or factual data about a business--the information being queried. This information is often numerical, additive measurements and can consist of many columns and millions or billions of rows. Dimension tables are usually smaller and hold descriptive data that reflects the dimensions, or attributes, of a business. SQL queries then use joins between fact and dimension tables and constraints on the data to return selected information."
    so from your explaination there are going to be 3 dimension tables
    Dim_Cust (Details about the customers) (Customer_ID,Cell No,Address)
    Dim_Book(Details about the Books) (Book Name ,ID,Genre)
    Dates (I am confused about the dates part)
    Fct_Book_Sales (Confused about this part also)
    and one last thing What would the fact table look like ??

  • Creation of star schema from snowflake schem in BMM layer

    hi,
    This is my situation.I have "Fact-table" which has Dim 1 .now Dim 1 is joined to Dim2,Dim3
    Fact
    |
    Dim 1
    |
    | |
    Dim 2 Dim 3
    Now in Bmm Layer how can i make this snowfalke schema to star schema.I heard about making changes in the Logical Table source.And what will be the look of the presentation layer.
    Any help is appricaited Guys.

    In physical layer, you have a join between Dim 1 and Dim 2, Dim1 and DIm3, Fact and Dim1. In BMM for Dim1, in the sources, add Dim2 and Dim3. You may add both these dimensions in one single LTS if the data is not duplicate in the tables. In case the data is duplicated add them as seperate LTS in the sources for Dim1. Refer this post for reference -- Logical Table source source query
    In BMM you need a join between Dim1 and Fact. Basically your Dim1 is sourced from three different tables which are your dimensions. This would transform your snowflake into star. In your presentation layer you will have all the columns from your dimensions (except for the duplicates, lets say you have column A in both dim1 and dim2, you should map this column in column mapping tab so as to enable BI server to pick the most economical source) and facts.
    Hope this clears your question.

  • Star Schema and EUL

    1. It's a prerequisite to use a star schema to build a EUL or I can/ must used a Relational Schema?
    2. The OLAP Option of Discoverer Plus work with an EUL or with a star schema
    3. Which components requiere the OLAP option that don't require the Relational Option (i.e. AW) ?
    4 I can generate a star schema as: a) a simple relational model where the FK key is a common domain for the fact and dimension table (i.e. Dept. Number) and having a table for each dimension (I don't speaking about time dimensions, but fields like barnch, dept., etc,). b) a star schema where the dimensions are grouped in tables depending on its significance (i.e. Producto, Channels, Time, etc). In this case I'll use a auto-generated sequential number as key for each table record, wich is referenced in the fact table. The question is, which is, in general, the best strategy 1.a ot 1.b. It depends of the size of the database?
    5. There is two bussines areas wich need the same information, but one of them, will used always a summarized version whit 60000 records (the other one will process more than 1000000 each time). No doubts in using two distincts set of tables to generate two distincts EULs or Star Schemas, in order to gain in performance?

    This is a more suitable question for the Business Intelligence (EBS).
    In the mean time, you may want to check the BI OBE: http://www.oracle.com/technology/obe/obe_bi/bi.html , as well as http://www.oracle.com/technology/products/bi/index.html, http://www.oracle.com/technology/documentation/bi_doc.html
    ~ Madrid.

  • "Reverse Star schema" to star schema

    Hey
    This is my first post and I´m working with OWB for abou 4 Months now.
    My problem:
    I am working with a cube but instead of a real star schema I always get a model like this:
    a fact in the fact table of my cube matches to multiple records in the dimensions. (1 to n)
    The cube itself is ok and even the results but on the database site I want to implement a real star schema.
    Is there any way to remodel the dimensions or the cube or tables so that i an get a star schema.
    I read about bridge tables to solve this problem, but I´m not sure they can help me.
    Anyone an idea?
    Thanks Mario

    See if this helps,
    http://docs.oracle.com/cd/E14571_01/bi.1111/e10540/busmodlayer.htm#BGBJGJIB
    http://kimballgroup.forumotion.net/t1356-weighting-factor-in-bridge-table

  • HR Analytics Star Schema Definitions

    All--
    We currently report on PeopleSoft data by extracting it into a data mart. ( The data store's configuration is not in a star schema format). We use it for day to day operational reporting needs. We are researching on HR Analytics and want to know more details about the data elements covered in the schemas, is there any document that explains the details of the various star schemas and the mappings to the original PeopleSoft database elements ?
    We need this to perform a gap analysis. Any help would be much appreciated.
    Thanks,
    Ajit

    Apparently on eDelivery they have finally made available the Source to Staging Mappings in spreadsheet form.
    Check that out.
    Bob Murching posted about it a few cycles ago on this forum as well.
    To clarify the document does not exactly detail the stars. You need to download the Data Model Reference Guide from Metalink3 to see those details.

  • Do we use direct star schema concept anywhere in sap bw

    i know about extended star schema,and where sap uses this concept.
    my question is do we use normal star schema concept any where in sap bw, apart from extended star schema concept.
    if yes specify the answer briefly .
    thanks in advance
    with regards
    yash.b

    Hi,
    If I'm not mistaken an Analytic view in Hana is more like the normal star schema, it is definitely not extended and can be consumed by BW for OLAP processing.
    Regards,
    Michael Devine

  • How to document your star-schemas and dashboards?

    Hello practitioners,
    We are new to OBIEE and started some weeks ago. We are a two-men team. One guy doing all the data design and the other for everything around Answers.
    So it happens regularly that the other guy has to ask the one guy, about the exact definition and meaning of data-fields, he wants to use in Answers.
    Being a real programmer the one guy only needs a proper, self-explainary field name as documentation, of course (or so he thought).
    Question:
    What tools and methods do you use to document the star-schemas and dashboards?
    Being the other guy, it is important, that I pick the correct fields, while on the other hand I do not want to disect a dashboard I built a while back, everytime somebody wants something simular, just to figure out what I actually did, back then...
    Thank you for your help
    Turalf
    Edited by: Turalf on Mar 24, 2010 12:03 PM

    Hi Turalf,
    Have you looked at the OBIEE Metadata Dictionary ? A method to allow answers users to gain access to column definitions, and you can view the mapping from Presentation, through BMM to Physical layer.
    Im pretty sure you can expose comments from the RPD into this also.
    http://obiee101.blogspot.com/2008/12/obiee-metadata-dictionary.html
    Maybe you could look at the ODI - OBIEE data lineage also, it provides "report to source" mapping info :
    http://www.oracle.com/technology/obe/fusion_middleware/ODI/OBI-ODI_Lineage/OBI-ODI_Lineage.htm
    Hope this helps.

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