OBIEE 11g Design Tips – The Best Practices


I had already composed the OBIEE design guidelines and best practices in my previous quite old post which mostly encircled the approach and best adopted strategies for previous release of OBIEE (aka Siebel Analytics 7.8.5) and OBIEE 10.1.3.4 version. Refer to my previous post :

https://debaatobiee.wordpress.com/category/obiee/best-practices/

Here are the design tips and guidelines to adhere as per Oracle recommended Metadata Repository Builders guide of OBIEE11g . The excerpt from it directly compiled like below:

Design Tips for the Physical Layer

  • It is recommended that you use table aliases frequently in the Physical layer to
    eliminate extraneous joins, including the following:
    – Eliminate all physical joins that cross dimensions (inter-dimensional circular
    joins) by using aliases.
    – Eliminate all circular joins (intra-dimensional circular joins) in a logical table
    source in the Physical Model by creating physical table aliases.
    For example, say you have a Customer table that can be used to look up
    ship-to addresses, and using a different join, to look up bill-to addresses.
    Avoid the circular joins by aliasing the table in the Physical layer so that there
    is one instance for each purpose, with separate joins.
  • You might import some tables into the Physical layer that you might not use right
    away, but that you do not want to delete. To identify tables that you do want to
    use right away in the Business Model and Mapping layer, you can assign aliases to
    physical tables before mapping them to the business model layer.
  • An opaque view (a Physical layer table that consists of a SELECT statement)
    should be used only if there is no other solution to your modeling problem.
    Ideally, a physical table should be created, or alternatively a materialized view.
    Opaque views prevent the Oracle BI Server from generating its own optimized
    SQL, because they contain fixed SQL statements that are sent to the underlying
    data source.

Design Tips for the Business Model and Mapping Layer

  • Create the business model with one-to-many logical joins between logical
    dimension tables and the fact tables wherever possible. The business model
    should ideally resemble a simple star schema in which each fact table is joined
    directly to its dimensions.
     Every logical fact table must join to at least one logical dimension table. Note that
    when the source is a fully denormalized table or flat file, you must map its
    physical fact columns to one or more logical fact tables, and its physical dimension
    columns to logical fact tables.
  • Every logical dimension table should have a dimensional hierarchy associated
    with it. This rule holds true even if the hierarchy has only one level, such as a
    scenario dimension {actual, forecast, plan}.
  • Make sure that all appropriate fact sources map to the proper level in the
    hierarchy using aggregation content. You set up aggregation content in the Levels
    tab of the Logical Column dialog for the measure. Note that this is different from
    the Content tab of the Logical Table Source dialog, which is used to specify the
    grain of the source tables to which it maps.
  • Typically, logical fact tables should not contain any keys. The only exception is
    when you need to send Logical SQL queries against the Oracle BI Server from a
    client that requires keys. In this case, you need to expose those keys in both the
    logical fact tables, and in the Presentation layer.
  • Normally, all columns in logical fact tables are aggregated measures, except for
    keys required by external clients, or dummy columns used as a divider. Other
    non-aggregated columns should instead exist in a logical dimension table.
  • In some situations, you might want to have multiple logical fact tables in a single
    business model. For Logical SQL queries, the multiple logical fact tables behave as
    if they are one table. 
  • You can define calculations in either of the following ways:
    – Before the aggregation, in the logical table source. For example:
    sum(col_A *( col_B))
    – After the aggregation, in a logical column derived from two other logical
    columns. For example:
    sum(col A) * sum(col B)
    You can also define post-aggregation calculations in Answers or in Logical SQL
    queries.
  • If you plan to use Oracle Scorecard and Strategy Management, it is a best practice
    to implement at least one time dimension in the Oracle BI repository you are using
    for your KPIs. This action is necessary because you use KPIs in scorecards to
    measure progress and performance over time. Note that an individual scorecard
    automatically picks up any dimension used by KPIs in that scorecard.
  • Aggregate sources should be created as separate logical table sources. For fact
    aggregates, use the Content tab of the Logical Table Source dialog to assign the
    correct logical level to each dimension.
  • Each dimension level in a hierarchy must have a unique level key. Also, each
    logical dimension table must have a unique primary key. Normally, this key is
    also used as the level key for the lowest hierarchy level.
  • Renaming columns in the Business Model and Mapping layer automatically
    creates aliases (synonyms) for Presentation layer columns that have the property
    Use Logical Column Name selected.
  • To prevent problems with aggregate navigation, ensure that each logical level of a
    dimension hierarchy contains the correct value in the field named Number of
    elements at this level. Fact sources are selected on a combination of the fields
    selected as well as the levels in the dimensions to which they map. By adjusting
    these values, you can alter the fact source selected by the Oracle BI Server. See
    “Creating Logical Levels in a Dimension” for more information about setting this
    value.

 Modeling Outer Joins
The following guidelines provide tips on how to model outer joins:

  • Due to the nature of outer joins, queries that use them are usually slower. Because
    of this, define outer joins only when necessary. Where possible, use ETL
    techniques to eliminate the need for outer joins in the reporting SQL.
  • Outer joins are always defined in the Business Model and Mapping layer. Physical
    layer joins do not specify inner or outer.
  • You can define outer joins by using logical table joins, or in logical table sources.
    Which type of outer join you use is determined by whether the physical join maps
    to a business model join, or to a logical table source join.
  • Be aware that outer joins in logical table sources are always included in a query,
    even if the none of the columns in one of the mapped physical tables are used.
    For example, assume that a logical table source is mapped to physical tables A and
    B. When no outer joins are defined, if physical table A is not required to satisfy a
    request, it is not included in the physical query. However, if the logical table
    source has an outer join defined to table A, table A is still included in the physical
    query, even if only physical table B is required to satisfy the request.
  • If you must define an outer join, try to create two separate dimensions, one that
    uses the outer join and one that does not. Make sure to name the dimension with
    the outer join in a way that clearly identifies it, so that client users can use it as
    little as possible.

 Design Tips for the Presentation Layer

  • You can show fewer columns than exist in the Business Model and Mapping layer.
    For example, you can exclude the key columns because they have no business
    meaning.
  • You can organize columns using a different structure from the table structure in
    the Business Model and Mapping layer.
  • You can display column names that are different from the column names in the
    Business Model and Mapping layer.
  • You can set permissions to grant or deny users access to individual subject areas,
    tables, and columns.
  • You can export logical keys to ODBC-based query and reporting tools.
  • You can create multiple subject areas for a single business model.
  • You can create a list of aliases (synonyms) for presentation objects that can be used
    in Logical SQL queries. This feature lets you change presentation column names
    without breaking existing reports.
    The following is a list of tips to use when designing the Presentation layer:
  • Because there is no automatic way to synchronize all changes between the
    Business Model and Mapping layer and the Presentation layer, it is best to wait
    until the Business Model and Mapping layer is relatively stable before adding
    customizations in the Presentation layer.
  • There are many ways to create subject areas, such as dragging and dropping the
    entire business model, dragging and dropping incremental pieces of the model, or
    automatically creating subject areas based on logical stars or snowflakes. See
    “Creating Subject Areas” for information about each of these methods. Dragging
    and dropping incrementally works well if certain parts of your business model are
    still changing.
  • It is a best practice to rename objects in the Business Model and Mapping layer
    rather than the Presentation layer, for better maintainability. Giving user-friendly
    names to logical objects rather than presentation objects ensures that the names
    can be reused in multiple subject areas. Also, it ensures that the names persist
    even when you need to delete and re-create subject areas to incorporate changes to
    your business model.
  • Be aware that members in a presentation hierarchy are not visible in the
    Presentation layer. Instead, you can see hierarchy members in Answers.
  • You can use the Administration Tool to update Presentation layer metadata to give
    the appearance of nested folders in Answers. See “Nesting Folders in Answers” for
    more information.
  • When setting up data access security for a large number of objects, consider
    setting object permissions by role rather than setting permissions for individual
    columns. See Chapter 13, “Applying Data Access Security to Repository Objects”
    for details.
  • When setting permissions on presentation objects, you can change the default
    permission by setting the DEFAULT_PRIVILEGES configuration setting in the
    NQSConfig.INI file. 

3 thoughts on “OBIEE 11g Design Tips – The Best Practices

  1. Hi Debashish,
    Thanks for the information above…It is really helpful.
    I have a query…why are joins required in the physical layer in addition to the imported joins from the data warehouse?

    Regards,
    Mahesh

    • Hi ,
      In dimensional modelling concept it might happen that your DB joins are not sufficient enough to satisfy your fact-dimensional modelling specially when you are using Surrogate keys .In those scenarios it is necessary to have physical layer joins . Apart from that when you need joins on multiple attributes more like complex joins your DB imported join doesn’t allow/support that . So you potentially need to rely on RPD Physical layer object based joins .
      Hope this clarifies .
      Thanks,
      D

      • Hi Debashis,
        I would need your clarification on the query below…
        For horizontal federation, when joining two fact tables via a common dimension, should they be of the same granularity?
        Thanks.
        Mahesh

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