Cause-Effect Graphing is a black box testing - Explain?

So many testing techniques have been categorized under the black box testing and the cause effect graphing is one of them and that is what the whole article is all about.

- A directed graph created for the purpose of mapping of the set of causes to a set of effects is nothing but a cause effect graph.
- The causes mapped in the graph are merely the input to a software system or application and the effects can be thought of as the corresponding outputs.
- The right of the cause effect graph houses all the effects with their corresponding nodes and the left side shelters all the causes and along with their corresponding nodes.
- A graph representing causes and effects in such a way is said to be a typical cause effect graph.
- It may also make use of certain intermediate nodes for the representation of the relation between the input and the output using the logical operators like AND, OR etc.
- The constraints can be effectively added to the effects and causes in the graph and these represented as the labelled edges using a dashed line along with the symbol of the constraint.

Constraint Symbols for the Causes:
1. E – exclusive
2. OaOO – one and only one
3. I – at least one

- The first constraint is used to state that at any instant any two causes (say cause 1 and cause 2) cannot be true simultaneously.
- The second constraint i.e., the inclusive constraint is used to state that at least one of the two or more numbers of causes must be true.
- The third constraint “one and only one” is used to state that the only one among all the constraints can be true.

Constraints for the Effects

1. R – requires
2. M – mask

- These are the only two valid constraints for the effects.
- The first one states that if one of the causes is true, then it implies that the other one also must be true and it also states that only one of the two constraints can be true and other can be false.
- The second constraint i.e., the mask constraint states just the opposite of the first constraint i.e., if one of the effects is true, then the other must be false.

"One point to be noted here is that the mask constraint only relates to the effects rather than relating to the causes like other constraints."

The direction of the graph is represented as shown below:
Causes -> Intermediate nodes -> Effects

Normal Forms of Cause Effect Graph

The cause effect graph is always rearranged in such a way that at any point between any input and output there lays only one node. Two normal forms of the cause effect graph have been identified:

- Conjunctive normal form
- Disjunctive normal form

When is Cause Effect Graphing performed?

One of the main purposes of the cause effect graph is the generation of the reduced decision table. The cause effect graphing is performed after the following tasks have been completed:

1. All the requirements have been reviewed to check out for any ambiguity.
2. All the requirements have been reviewed for their content.
3. It has been ensured that the requirements are complete and correct.

Cause effect graphing is basically used for hardware testing, but now it has been adopted for the use in the software testing.

It takes in to consideration only the desired external behaviour of the system and therefore it has been categorized as a black box testing technique and only selects the test cases that represent a logical relation between the causes and effects for the production of the test cases.

Database Recovery Techniques - Overview

The main goal of recovery is to ensure the atomicity property of a transaction. If a transaction fails before completing its execution, the recovery mechanism has to make sure that the transaction has no lasting effects on the database. The different approaches to recovery :
- Deferred Update : These techniques postpone any actual updating of the database on disk until a transaction reaches its commit point. The transaction force writes the log to disk before recording the updates in the database. This approach, when used with certain concurrency control methods, is designed never to require transaction rollback, and recovery simply consists of redoing the operations of transactions committed after the last checkpoint from the log.
Disadvantage : Too much buffer space may be needed, since updates are kept in the buffers and are not applied to disk until a transaction commits.
Deferred update can lead to a recovery algorithm known as NO-UNDO/REDO. Immediate update techniques may apply changes to the database on disk before the transaction reaches a successful conclusion. Any changes applied to the database must be first recorded in the log and force-written to disk so that these operations can be undone if necessary.
- Another algorithm, known as UNDO/NO-REDO, can also be developed for immediate update if all transaction actions are recorded in the database before commit.
- There is another technique, called shadow paging technique, which keeps track of old database pages by using a shadow directory. This technique, which is classified as NO UNDO/NO-REDO, does not require a log in single-user systems but still needs the log for multiuser systems.
- ARIES, a specific recovery scheme is used in some of IBM's relational database products.
- Two-phase commit protocol is used for recovery from failures involving multi-database transactions.
- Recovery from catastrophic failures is typically done by backing up the database and the log to tape. The log can then be backed up more frequently than the database, and the backup log can be used to redo operations starting from the last database backup.