BOBJ - LoopsAboutLoop is aBOBJ - Join Path (or Query Path)problem which is a set of joins that defines a closed path through a set of tables in a schema.

You often useBOBJ - Contextin schema that contain multiple fact tables (multiple stars) that share lookup tables.Articles Related BOBJ - Alias dat:bobj:bobj_alias dat:bobj:bobj_aliases BOBJ - Chasm Traps (converging many to one joins) BOBJ - Joins (Home) BOBJ - Join Path (or Query Path) Data Modeling - Issue (SQL Trap)How Does a Loop Affect Queries?If you created a universe based on the above structure, any query run against the tables in the loop would return only results where the country values for resorts and the country values for customer origin are equivalent. This double restriction on the shared lookup Country table returns fewer rows than expected.Result ExpectedResult received

Country is serving two purposes: Lookup for the resort country. Lookup for the customer country of origin.This creates a restriction so that data is returned only when the resort country is the same as the customer country. The resulting report shows only the number of visitors from the US who visited resorts in the US.Breaking a loopDepending on the nature of the loop, you can resolve the loop in Designer using either an alias to break the join path, or a context to separate the two join paths so that a query can only take one path or the other.With an aliasYou create anBOBJ - Aliasfor Country and rename it Country_Region. The two one ended joins are now separated as follows: Country keeps a join to the Resort table. Country_Region is joined to the Region table.The schema now appears as shown below:

Aliasare not appropriate in such schema. See Context section for the explanation.With a contextAfter the creation of an alias, the addition of a new table can create a new loop join as shown below :You must continue creating aliases for each new table you add to the schema. This is difficult to maintain, and also ends up proliferating the number of similar objects using each table in the universe.The only way to resolve this loop is to leave the loop in place, and create a context that specifies one or the other path around the schema. This ensures that queries answer questions for one transaction or the other, such as: Is the customer information needed from the perspective of sales or reservations?You then create different sets of objects from the tables in the different contexts. Users can then run either : Reservation queries or Sales queries,

You often useBOBJ - Contextin schema that contain multiple fact tables (multiple stars) that share lookup tables.Detected by Detect Aliases (Tools > Automated Detection > Detect Aliases) Detect Contexts (Tools > Automated Detection > Detect Context) Detect Loops (Tools > Automated Detection > Detect Loops) Check Integrity Visual analysis of schemaSolved byCreatingBOBJ - AliasandBOBJ - Contextto break loops.

BOBJ - AliasAboutAliases are references to existing tables in a schema. An Alias is a table that is an exact duplicate of the original table (base table), with a different name.Articles Related BOBJ - Fan Trap (serial many to one joins) BOBJ - Joins (Home) BOBJ - Loops BOBJ - Context BOBJ - Join Path (or Query Path)Why using alias ?You use aliases for two main reasons: To solveBOBJ - LoopsandBOBJ - Fan Trap (serial many to one joins)join path problem To use the table more than once in a query. To abbreviate the table name to save typing when writing freehandSQL.The exampleBeach universecontains 2 aliases; Resort_Country for Country, and Sponsor for Customer.Another possible use of aliases is to create an alias for each table as it is inserted into the schema. You then build the schema using the alias tables, not the original base tables. You place the base tables together away from the main universe structure. This allows you to give meaningful names to tables, and prevents the need to rebuild major sections of a universe structure should a base table need to be aliased at a later stage.Managing AliasCreation Select the table inBusiness Object - Universe Designer Menu > Insert > AliasDelete Click an alias and select Edit > Clear.List Menu > Tools > List of AliasesStructure PaneTo avoid confusing base tables with aliases, you can display the alias with the name of the base table it represents in the table title as follows: Select Tools > Options > Graphics, and then select the Aliased Name check box

BOBJ - ContextAboutContexts are a collection ofjoinswhich provide a validquery pathforSAP BO - Web Intelligenceto generateSQL.

Articles Related BOBJ - Cardinalities BOBJ - Chasm Traps (converging many to one joins) BOBJ - Fan Trap (serial many to one joins) BOBJ - Joins (Home) BOBJ - Loops BOBJ - Join Path (or Query Path)UseYou use contexts to resolvejoin problemsthat can return too many or too few rows because of the way that tables are linked in the target database.You need to verify thatcardinalitiyare correctly set for all joins in your schema to ensure that you have the correct contexts, and that you have valid join paths.Settingcardinalitiycan also help you understand how tables are related in the database, and to graphically identify potential join path problems in your schema.To solve loopThe most common use of contexts is to separate twoquery paths, so that one query returns data for one fact table, and the other query returns data for another fact table. You use contexts to direct join paths in a schema which contains multiple fact tables.Aliasare not appropriate in such schema.You often use context in schema that contain multiple fact tables (multiple stars) that share lookup tables.To solve chasm and fan trapsContexts are also used to solve potentialBOBJ - Chasm Traps (converging many to one joins). These can occur when two many-to-one join paths converge on a single table. Multiple rows can be returned for a single dimension causing inflated results. Contexts can split out the query so that the correct number of rows are returned for the dimension. Contexts can also be used withBOBJ - Aliasto solveBOBJ - Fan Trap (serial many to one joins).Using contexts to determine AggregateAwareness incompatibilityYou can use contexts to exclude objects that are not compatible with an object using the @AggregateAware function in its definition, from being used in a query with the aggregate aware object.Managing ContextCreationAutomatically with Detect ContextTools > Automated Detection >Detect Contexts

Detect Contexts examines the many to one joins in the schema. It picks up the table that receives converging many to one joins and proposes contexts to separate the queries run on the table.Manually Insert > ContextEdit View > List Mode Double click a context name in the Contexts list pane. The Edit Context box appears

Delete Ensure that List mode is active (Select View > List Mode). Right click a context name in the Contexts list box and select Clear from the contextual menu.RenameClick a context and click the Rename button.SupportOne-to-one cardinality preventing context detectionA one-to one-cardinality positioned at the end of a join path can prevent Context Detection in Designer from detecting a context. You resolve this problem by changing the cardinality of the table at the end of the join path to one-to-many.Incompatible queryObjects from two different contexts are combined in a query. The two Select statements are synchronized to display returned data in separate tables.To allow incompatible queries to be run in Web Intelligence, you must select the MultipleSQLstatements in Designer for each context option. File > Parameters. Click theSQLtab. Select the MultipleSQLstatements for each context check box

BOBJ -ChasmTraps (converging many to one joins)AboutChasmTrapsis see as aJoin Pathproblem or data modeling issue(convergence type ) which returns more data than expected by returning acartesian product.Achasmtrapis a type of join path between three tables when twomany-to-onejoins converge on a single table, and there is nocontextin place that separates the converging join paths.

Achasmtrapinflates results without warningArticles Related BOBJ - Joins (Home) BOBJ - Context BOBJ - Join Path (or Query Path)ExampleThechasmtrapcauses a query to return every possible combination of rows for one measurewithevery possible combination of rows for the other measure.Measure only on the first fact table

Measure only on the second fact table

Measures on the two fact tables return incorrect result (cartesian product) :The query returns every possible combination of Number of Guests rowswithevery possible combination of Number of Future Guests rows: the Number of Guests transactions each appears twice, and the Number of Future Guests transactions each appears three times.

Detected by Visual analysis of table schema.UnlikeBOBJ - Loops,chasmtraps are not detected automatically byBusiness Object - Universe Designer, however, you can use DetectBOBJ - Context(Tools > Detect Contexts) to automatically detect and propose candidate contexts in your schema.Solved by Creating aBOBJ - Context. Using the feature MultipleSQLstatements for each measure. (File > Parameters >SQLtab )

Creating multipleSAP BOBJ - Universe(SAP BO - Web Intelligenceonly).

BOBJ - Fan Trap (serial many to one joins)AboutThisBOBJ - Join Path (or Query Path)problem return too many rows.A fan trap is a type of join path between three tables when a one-to-many join links a table which is in turn linked by another one-to-many join. This type of schema is commonly use to define aMany-to-many relationship.The fanning out effect of one-to-many joins can cause incorrect results to be returned when a query includes objects based on both tables.A simple example of a fan trap is shown below:

The many-to-many relationshipFor one sale_id, you have more than one model_id and for one model_id, you can have more than one saled_id. This rule is also true for the colour.Articles Related BOBJ - Alias dat:bobj:bobj_alias dat:bobj:bobj_aliases BOBJ - Joins (Home) BOBJ - Context BOBJ - Join Path (or Query Path)ExampleReport without sale model column

Report with sale model column

Solved byThe original query which returned the Cartesian product for Wendy Craig, must return the following table when run with the above solution:

Using an alias and contextThe fan trap using dimension objects in the query is solved by using anBOBJ - AliasandBOBJ - Context.

And multipleSQLStatements for Each Context checked (File > Parameters > SQl Tab)

Using Multiple SQL Statements for each measureIf you have only measure objects defined for both tables at the many end of the serial one-to-many joins, then you can use the Universe Parameters option MultipleSQLStatements for Each Measure.MultipleSQLStatements for Each Measure checked (File > Parameters > SQl Tab)

This forces the generation of separateSQLqueries for each measure that appears in the Query pane.You cannot use this method to generate multiple queries for dimensions. If an end user can include dimensions from any of the tables that reference the measure objects in the query, then you must use an alias and context to resolve the fan trap.Detected by Visual analysis of table schema.You cannot automatically detect fan traps. You need to visually examine the direction of the cardinalities displayed in the table schema.http://gerardnico.com/wiki/dat/bobj/bobj_loopshttp://gerardnico.com/wiki/dat/bobj/aliashttp://gerardnico.com/wiki/dat/bobj/contexthttp://gerardnico.com/wiki/dat/bobj/bobj_chasm_trapshttp://gerardnico.com/wiki/dat/bobj/bobj_fan_traps