1) What are the Back ground processes in Oracle and what are they.
1) This is one of the most frequently asked question.There are basically 9 Processes but in a
general system we need to mention the first five background processes.They do the house keeping activities for the Oracle and are common in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is commited.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo log file.
c) System Monitor(SMON) :: The System Monitor performs instance recovery at instance startup.This is useful for recovery from system failure
d)Process Monitor(PMON) :: The Process Monitor peforms process recovery when user Process fails. Pmon Clears and Frees resources that process was using.
e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate the
most recent checkpoint
f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal when they are busy.
g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network
h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture
i) Lckn :: We can have upto 10 lock processes for inter instance locking in parallel sql.
2) How many types of Sql Statements are there in Oracle
2) There are basically 6 types of sql statments.They are
a) Data Defination Language(DDL) :: The DDL statments define and maintain objects and drop objects.
b) Data Manipulation Language(DML) :: The DML statments manipulate database data.
c) Transaction Control Statements :: Manage change by DML
d) Session Control :: Used to control the properties of current session enabling and disabling roles and changing .e.g :: Alter Statements,Set Role
e) System Control Statements :: Change Properties of Oracle Instance .e.g:: Alter System
f) Embedded Sql :: Incorporate DDL,DML and T.C.S in Programming Language.e.g:: Using the Sql Statements in languages such as 'C', Open,Fetch, execute and close
3) What is a Transaction in Oracle
3) A transaction is a Logical unit of work that compromises one or more SQL Statements executed by a single User. According to ANSI, a transaction begins with first executable statment and ends when it is explicitly commited or rolled back.
4) Key Words Used in Oracle
4) The Key words that are used in Oracle are ::
a) Commiting :: A transaction is said to be commited when the transaction makes permanent changes resulting from the SQL statements.
b) Rollback :: A transaction that retracts any of the changes resulting from SQL statements in Transaction.
c) SavePoint :: For long transactions that contain many SQL statements, intermediate markers or savepoints are declared. Savepoints can be used to divide a transactino into smaller points.
d) Rolling Forward :: Process of applying redo log during recovery is called rolling forward.
e) Cursor :: A cursor is a handle ( name or a pointer) for the memory associated with a specific stament. A cursor is basically an area allocated by Oracle for executing the Sql Statement. Oracle uses an implicit cursor statement for Single row query and Uses Explcit cursor for a multi row query.
f) System Global Area(SGA) :: The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance.It consists of Database Buffer Cache and Redo log Buffer.
g) Program Global Area (PGA) :: The PGA is a memory buffer that contains data and control information for server process.
g) Database Buffer Cache :: Databese Buffer of SGA stores the most recently used blocks of datatbase data.The set of database buffers in an instance is called Database Buffer Cache.
h) Redo log Buffer :: Redo log Buffer of SGA stores all the redo log entries.
i) Redo Log Files :: Redo log files are set of files that protect altered database data in memory that has not been written to Data Files. They are basically used for backup when a database crashes.
j) Process :: A Process is a 'thread of control' or mechansim in Operating System that executes series of steps.
5) What are Procedure,functions and Packages
5) Procedures and functions consist of set of PL/SQL statements that are grouped together as a unit to solve a specific problem or perform set of related tasks.
Procedures do not Return values while Functions return one One Value
Packages :: Packages Provide a method of encapsulating and storing related procedures, functions, variables and other Package Contents
6) What are Database Triggers and Stored Procedures
6) Database Triggers :: Database Triggers are Procedures that are automatically executed as a result of insert in, update to, or delete from table.
Database triggers have the values old and new to denote the old value in the table before it is deleted and the new indicated the new value that will be used. DT are useful for implementing complex business rules which cannot be enforced using the integrity rules.We can have the trigger as Before trigger or After Trigger and at Statement or Row level.
e.g:: operations insert,update ,delete 3
before ,after 3*2 A total of 6 combinatons
At statment level(once for the trigger) or row level( for every execution ) 6 * 2 A total of 12.
Thus a total of 12 combinations are there and the restriction of usage of 12 triggers has been lifted from Oracle 7.3 Onwards.
Stored Procedures :: Stored Procedures are Procedures that are stored in Compiled form in the database.The advantage of using the stored procedures is that many users can use the same procedure in compiled and ready to use format.
7) How many Integrity Rules are there and what are they
7) There are Three Integrity Rules. They are as follows ::
a) Entity Integrity Rule :: The Entity Integrity Rule enforces that the Primary key cannot be Null
b) Foreign Key Integrity Rule :: The FKIR denotes that the relationship between the foreign key and the primary key has to be enforced.When there is data in Child Tables the Master tables cannot be deleted.
c) Business Integrity Rules :: The Third Intigrity rule is about the complex business processes which cannot be implemented by the above 2 rules.
8) What are the Various Master and Detail Relation ships.
8) The various Master and Detail Relationship are
a) NonIsolated :: The Master cannot be deleted when a child is exisiting
b) Isolated :: The Master can be deleted when the child is exisiting
c) Cascading :: The child gets deleted when the Master is deleted.
9) What are the Various Block Coordination Properties
9) The various Block Coordination Properties are
Default Setting. The Detail records are shown when the Master Record are shown.
b) Deffered with Auto Query
Oracle Forms defer fetching the detail records until the operator navigates to the detail block.
c) Deffered with No Auto Query
The operator must navigate to the detail block and explicitly execute a query
10) What are the Different Optimisation Techniques
10) The Various Optimisation techniques are
a) Execute Plan :: we can see the plan of the query and change it accordingly based on the indexes
b) Optimizer_hint ::
Select /*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept
where (Deptno > 25)
c) Optimize_Sql ::
By setting the Optimize_Sql = No, Oracle Forms assigns a single cursor for all SQL statements.This slow downs the processing because for evertime the SQL must be parsed whenver they are executed.
f45run module = my_firstform userid = scott/tiger optimize_sql = No
d) Optimize_Tp ::
By setting the Optimize_Tp= No, Oracle Forms assigns seperate cursor only for each query SELECT statement. All other SQL statements reuse the cursor.
f45run module = my_firstform userid = scott/tiger optimize_Tp = No
11) How do u implement the If statement in the Select Statement
11) We can implement the if statement in the select statement by using the Decode statement.
e.g select DECODE (EMP_CAT,'1','First','2','Second'Null);
Here the Null is the else statement where null is done .
12)How many types of Exceptions are there
12) There are 2 types of exceptions. They are
a) System Exceptions
e.g. When no_data_found, When too_many_rows
b) User Defined Exceptions
e.g. My_exception exception
When My_exception then
13) What are the inline and the precompiler directives
13) The inline and precompiler directives detect the values directly
14) How do you use the same lov for 2 columns
14) We can use the same lov for 2 columns by passing the return values in global values and using the global values in the code
15) How many minimum groups are required for a matrix report
15) The minimum number of groups in matrix report are 4
16) What is the difference between static and dynamic lov
16) The static lov contains the predetermined values while the dynamic lov contains values that come at run time
17) What are snap shots and views
17) Snapshots are mirror or replicas of tables. Views are built using the columns from one or more tables. The Single Table View can be updated but the view with multi table cannot be updated
18) What are the OOPS concepts in Oracle.
18) Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorise the properties by setting the visual attributes and then attach the property classes for the
objects. OOPS supports the concepts of objects and classes and we can consider the peroperty classes as classes and the items as objects
19) What is the difference between candidate key, unique key and primary key
19) Candidate keys are the columns in the table that could be the primary keys and the primary key
is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table.
20)What is concurrency
20) Cuncurrency is allowing simultaneous access of same data by different users. Locks useful for accesing the database are
The exclusive lock is useful for locking the row when an insert,update or delete is being done.This lock should not be applied when we do only select from the row.
b) Share lock
We can do the table as Share_Lock as many share_locks can be put on the same resource.
21) Previleges and Grants
21) Previleges are the right to execute a particulare type of SQL statements.
e.g :: Right to Connect, Right to create, Right to resource
Grants are given to the objects so that the object might be accessed accordingly.The grant has to be
given by the owner of the object.
22)Table Space,Data Files,Parameter File, Control Files
22)Table Space :: The table space is useful for storing the data in the database.When a database is created two table spaces are created.
a) System Table space :: This data file stores all the tables related to the system and dba tables
b) User Table space :: This data file stores all the user related tables
We should have seperate table spaces for storing the tables and indexes so that the access is fast.
Data Files :: Every Oracle Data Base has one or more physical data files.They store the data for the database.Every datafile is associated with only one database.Once the Data file is created the size cannot change.To increase the size of the database to store more data we have to add data file.
Parameter Files :: Parameter file is needed to start an instance.A parameter file contains the list of instance configuration parameters e.g.::
db_block_buffers = 500
db_name = ORA7
db_domain = u.s.acme lang
Control Files :: Control files record the physical structure of the data files and redo log files
They contain the Db name, name and location of dbs, data files ,redo log files and time stamp.
23) Physical Storage of the Data
23) The finest level of granularity of the data base are the data blocks.
Data Block :: One Data Block correspond to specific number of physical database space
Extent :: Extent is the number of specific number of contigious data blocks.
Segments :: Set of Extents allocated for Extents. There are three types of Segments
a) Data Segment :: Non Clustered Table has data segment data of every table is stored in
cluster data segment
b) Index Segment :: Each Index has index segment that stores data
c) Roll Back Segment :: Temporarily store 'undo' information
24) What are the Pct Free and Pct Used
24) Pct Free is used to denote the percentage of the free space that is to be left when creating a table. Similarly Pct Used is used to denote the percentage of the used space that is to be used when creating a table
eg.:: Pctfree 20, Pctused 40
25) What is Row Chaining
25) The data of a row in a table may not be able to fit the same data block.Data for row is stored in a chain of data blocks .
26) What is a 2 Phase Commit
26) Two Phase commit is used in distributed data base systems. This is useful to maintain the integrity of the database so that all the users see the same values. It contains DML statements or Remote Procedural calls that reference a remote object. There are basically 2 phases in a 2 phase commit.
a) Prepare Phase :: Global coordinator asks participants to prepare
b) Commit Phase :: Commit all participants to coordinator to Prepared, Read only or abort Reply
27) What is the difference between deleting and truncating of tables
27) Deleting a table will not remove the rows from the table but entry is there in the database dictionary and it can be retrieved But truncating a table deletes it completely and it cannot be retrieved.
28) What are mutating tables
28) When a table is in state of transition it is said to be mutating. eg :: If a row has been deleted then the table is said to be mutating and no operations can be done on the table except select.
29) What are Codd Rules
29) Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only Rdbms to satisfy the maximum number of rules.
30) What is Normalisation
30) Normalisation is the process of organising the tables to remove the redundancy.There are mainly 5 Normalisation rules.
a) 1 Normal Form :: A table is said to be in 1st Normal Form when the attributes are atomic
b) 2 Normal Form :: A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key
c) 3rd Normal Form :: A table is said to be third Normal form when it is not dependant transitively
31) What is the Difference between a post query and a pre query
31) A post query will fire for every row that is fetched but the pre query will fire only once.
32) Deleting the Duplicate rows in the table
32) We can delete the duplicate rows in the table by using the Rowid
33) Can U disable database trigger? How?
33) Yes. With respect to table
ALTER TABLE TABLE
[ DISABLE all_trigger ]
34) A pseudocolumn behaves like a table column, but is not actually
stored in the table. You can select from pseudocolumns, but you
cannot insert, update, or delete their values. This section
describes these pseudocolumns:
35) How many columns can table have?
The number of columns in a table can range from 1 to 254.
36) Is space acquired in blocks or extents ?
In extents .
37) what is clustered index?
In an indexed cluster, rows are stored together based on their cluster key values .
Can not applied for HASH.
38) what are the datatypes supported By oracle (INTERNAL)?
Varchar2, Number,Char , MLSLABEL.
39 ) What are attributes of cursor?
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT
40) Can you use select in FROM clause of SQL select ?
1) Which trigger are created when master -detail rela?
1) master delete property
* NON-ISOLATED (default)
a) on check delete master
b) on clear details
c) on populate details
a) on clear details
b) on populate details
b) on clear details
c) on populate details
2) which system variables can be set by users?
3) What are object group?
An object group is a container for a group of objects. You define an object group when you want to package related objects so you can copy or reference them in another module.
4) What are referenced objects?
Referencing allows you to create objects that inherit their functionality and appearance from other objects.
Referencing an object is similar to copying an object, except that the resulting reference object maintains a
link to its source object. A reference object automatically inherits any changes that have been made to the
source object when you open or regenerate the module that contains the reference object.
5) Can you store objects in library?
Referencing allows you to create objects that inherit their functionality and appearance from other
objects. Referencing an object is similar to copying an object, except that the resulting reference
object maintains a link to its source object. A reference object automatically inherits any changes that
have been made to the source object when you open or regenerate the module that contains the
yes , partially. 1) PROPERTY CLASS - inheritance property
2) OVERLOADING : procedures and functions.
7) Can you issue DDL in forms?
yes, but you have to use FORMS_DDL.
Referencing allows you to create objects that inherit their functionality and appearance from other
objects. Referencing an object is similar to copying an object, except that the resulting reference object
maintains a link to its source object. A reference object automatically inherits any changes that have
been made to the source object when you open or regenerate the module that contains the reference object.
Any string expression up to 32K:
· an expression or a variable representing the text of a block of dynamically created PL/SQL code
· a DML statement or
· a DDL statement
The statement you pass to FORMS_DDL may not contain bind variable references in the string, but the
values of bind variables can be concatenated into the string before passing the result to FORMS_DDL.
8) What is SECURE property?
8)- Hides characters that the operator types into the text item. This setting is typically used for
9 ) What are the types of triggers and how the sequence of firing in text item
Triggers can be classified as Key Triggers, Mouse Triggers ,Navigational Triggers.
Key Triggers :: Key Triggers are fired as a result of Key action.e.g :: Key-next-field, Key-up,Key-Down
Mouse Triggers :: Mouse Triggers are fired as a result of the mouse navigation.e.g. When-mouse-button-presed,when-mouse-doubleclicked,etc
Navigational Triggers :: These Triggers are fired as a result of Navigation. E.g : Post-Text-item,Pre-text-item.
We also have event triggers like when –new-form-instance and when-new-block-instance.
We cannot call restricted procedures like go_to(‘my_block.first_item’) in the Navigational triggers
But can use them in the Key-next-item.
The Difference between Key-next and Post-Text is an very important question. The key-next is fired as a result of the key action while the post text is fired as a result of the mouse movement. Key next will not fire unless there is a key event.
The sequence of firing in a text item are as follows ::
a) pre - text
b) when new item
d) when validate
e) post text
10 ) Can you store pictures in database? How?
10)Yes , in long Raw datatype.
11) What are property classes ? Can property classes have trigger?
11) Property class inheritance is a powerful feature that allows you to quickly define objects that conform to
your own interface and functionality standards. Property classes also allow you to make global changes to
applications quickly. By simply changing the definition of a property class, you can change the definition
of all objects that inherit properties from that class.
Yes . All type of triggers .
* 12 a) If you have property class attached to an item and you have same trigger written for the item .
Which will fire first?
12)Item level trigger fires , If item level trigger fires, property level trigger won't fire. Triggers at the lowest level are always given the first preference. The item level trigger fires first and then the block and then the Form level trigger.
13) What are record groups ? * Can record groups created at run-time?
13)A record group is an internal Oracle Forms data structure that has a column/row framework similar to a
database table. However, unlike database tables, record groups are separate objects that belong to the
form module in which they are defined. A record group can have an unlimited number of columns of type
CHAR, LONG, NUMBER, or DATE provided that the total number of columns does not exceed 64K.
Record group column names cannot exceed 30 characters.
Programmatically, record groups can be used whenever the functionality offered by a two-dimensional
array of multiple data types is desirable.
TYPES OF RECORD GROUP:
Query Record Group A query record group is a record group that has an associated SELECT statement.
The columns in a query record group derive their default names, data types, and lengths from the database columns referenced in the SELECT statement. The records in a query record group are the rows retrieved by the query associated with that record group.
Non-query Record Group A non-query record group is a group that does not have an associated query, but whose structure and values can be modified programmatically at runtime.
Static Record Group A static record group is not associated with a query; rather, you define its
structure and row values at design time, and they remain fixed at runtime.
14) What are ALERT?
14)An ALERT is a modal window that displays a message notifiying operator of some application
15) Can a button have icon and lable at the same time ?
16) What is mouse navigate property of button?
When Mouse Navigate is True (the default), Oracle Forms performs standard navigation to move the focus
to the item when the operator activates the item with the mouse.
When Mouse Navigate is set to False, Oracle Forms does not perform navigation (and the resulting validation) to move to the item when an operator activates the item with the mouse.
17) What is FORMS_MDI_WINDOW?
17) forms run inside the MDI application window. This property is useful for calling a form from another one.
18) What are timers ? when when-timer-expired does not fire?
18) The When-Timer-Expired trigger can not fire during trigger, navigation, or transaction processing.
19 ) Can object group have a block?
19)Yes , object group can have block as well as program units.
20) How many types of canvases are there.
20)There are 2 types of canvases called as Content and Stack Canvas. Content canvas is the default and the one that is used mostly for giving the base effect. Its like a plate on which we add items and stacked canvas is used for giving 3 dimensional effect.
1) What are user-exits?
1) It invokes 3GL programs.
2) Can you pass values to-and-fro from foreign function ? how ?
2) Yes . You obtain a return value from a foreign function by assigning the return value to an Oracle Forms
variable or item. Make sure that the Oracle Forms variable or item is the same data type as the return value
from the foreign function.
After assigning an Oracle Forms variable or item value to a PL/SQL variable, pass the PL/SQL variable as
a parameter value in the PL/SQL interface of the foreign function. The PL/SQL variable that is passed as
a parameter must be a valid PL/SQL data type; it must also be the appropriate parameter type as defined
in the PL/SQL interface.
3) What is IAPXTB structure ?
3) The entries of Pro * C and user exits and the form which simulate the proc or user_exit are stored in IAPXTB table in d/b.
4) Can you call WIN-SDK thruo' user exits?
5) Does user exits supports DLL on MSWINDOWS ?
5) YES .
6) What is path setting for DLL?
6) Make sure you include the name of the DLL in the FORMS45_USEREXIT variable of the ORACLE.INI file, or rename the DLL to F45XTB.DLL. If you rename the DLL to F45XTB.DLL, replace the existing F45XTB.DLL in the \ORAWIN\BIN directory with the new F45XTB.DLL.
7) How is mapping of name of DLL and function done?
7) The dll can be created using the Visual C++ / Visual Basic Tools and then the dll is put in the
path that is defined the registery.
8) what is precompiler?
8) It is similar to C precompiler directives.
9) Can you connect to non - oracle datasource ? How?
9) Yes .
10 ) what are key-mode and locking mode properties? level ?
10) Key Mode : Specifies how oracle forms uniquely identifies rows in the database.This is property includes
for application that will run against NON-ORACLE datasources .
Key setting unique (default.)
Locking mode :
Specifies when Oracle Forms should attempt to obtain database locks on rows that correspond to queried records in the form.
a) immediate b) delayed
11) What are savepoint mode and cursor mode properties ? level?
11) Specifies whether Oracle Forms should issue savepoints during a session. This property is included primarily for applications that will run against non-ORACLE data sources. For applications that will run against ORACLE, use the default setting.
Cursor mode - define cursur state across transaction
13) Identifies a block as transactional control block. i.e. non - database block that oracle forms should manage as transactional block.(NON-ORACLE datasource) default - FALSE.
14) What is OLE automation ?
14) OLE automation allows an OLE server application to expose a set of commands and functions that can be
invoked from an OLE container application. OLE automation provides a way for an OLE container application to use the features of an OLE server application to manipulate an OLE object from the OLE container environment. (FORMS_OLE)
15) What does invoke built-in do?
15) This procedure invokes a method.
list list_type := 0);
object Is an OLE2 Automation Object.
method Is a method (procedure) of the OLE2 object.
list Is the name of an argument list assigned to the OLE2.CREATE_ARGLIST function.
16) What are OPEN_FORM,CALL_FORM,NEW_FORM? diff?
16) CALL_FORM : It calls the other form. but parent remains active, when called form completes the operation , it releases lock and control goes back to the calling form.
When you call a form, Oracle Forms issues a savepoint for the called form. If the CLEAR_FORM function
causes a rollback when the called form is current, Oracle Forms rolls back uncommitted changes to this
OPEN_FORM : When you call a form, Oracle Forms issues a savepoint for the called form. If the
CLEAR_FORM function causes a rollback when the called form is current, Oracle Forms rolls back
uncommitted changes to this savepoint.
NEW_FORM : Exits the current form and enters the indicated form. The calling form is terminated as
the parent form. If the calling form had been called by a higher form, Oracle Forms keeps the higher call
active and treats it as a call to the new form. Oracle Forms releases memory (such as database cursors)
that the terminated form was using.
Oracle Forms runs the new form with the same Runform options as the parent form. If the parent form was
a called form, Oracle Forms runs the new form with the same options as the parent form.
17 ) What is call form stack?
17) When successive forms are loaded via the CALL_FORM procedure, the resulting module hierarchy is known as the call form stack.
18) Can u port applictions across the platforms? how?
18) Yes we can port applications across platforms.Consider the form developed in a windows system.The form would be generated in unix system by using f45gen my_form.fmb scott/tiger
1) What is a visual attribute?
1) Visual attributes are the font, color, and pattern properties that you set for form and menu objects that appear in your application's interface.
2) Diff. between VAT and Property Class? imp
2)Named visual attributes define only font, color, and pattern attributes; property classes can contain these and any other properties.
You can change the appearance of objects at runtime by changing the named visual attribute
programmatically; property class assignment cannot be changed programmatically.
When an object is inheriting from both a property class and a named visual attribute, the named visual
attribute settings take precedence, and any visual attribute properties in the class are ignored.
3 ) Which trigger related to mouse?
4) What is Current record attribute property?
4) Specifies the named visual attribute used when an item is part of the current record.
Current Record Attribute is frequently used at the block level to display the current row in a multi-record
If you define an item-level Current Record Attribute, you can display a pre-determined item in a special color
when it is part of the current record, but you cannot dynamically highlight the current item, as the input focus changes.
5) Can u change VAT at run time?
5) Yes. You can programmatically change an object's named visual attribute setting to change the font, color,
and pattern of the object at runtime.
6) Can u set default font in forms?
6) Yes. Change windows registry(regedit). Set form45_font to the desired font.
7) Can u have OLE objects in forms?
8) Can u have VBX and OCX controls in forms ?
9) What r the types of windows (Window style)?
9) Specifies whether the window is a Document window or a Dialog window.
10) What is OLE Activation style property?
10) Specifies the event that will activate the OLE containing item.
11) Can u change the mouse pointer ? How?
11) Yes. Specifies the mouse cursor style. Use this property to dynamically change the shape of the cursor.
1) How many types of columns are there and what are they
1) Formula columns :: For doing mathematical calculations and returning one value
Summary Columns :: For doing summary calculations such as summations etc.
Place holder Columns :: These columns are useful for storing the value in a variable
2) Can u have more than one layout in report
2) It is possible to have more than one layout in a report by using the additional layout option in the layout editor.
3) Can u run the report with out a parameter form
3) Yes it is possible to run the report without parameter form by setting the PARAM value to Null
4) What is the lock option in reports layout
4) By using the lock option we cannot move the fields in the layout editor outside the frame. This is useful for maintaining the fields .
5) What is Flex
5) Flex is the property of moving the related fields together by setting the flex property on
6) What are the minimum number of groups required for a matrix report
6) The minimum of groups required for a matrix report are 4