Question

Explain why the following requirement is not sufficient. How would you amend it? "The order entry system shall not crash more than 5 times per year. The system shall recover from each crash as quickly as possible to avoid down time."

Short answer

The requirement lacks specificity on crash types and recovery time. Amend it by specifying crash types and recovery times.

Step-by-step solution

Understanding the Initial Requirement

The requirement states that the order entry system should crash no more than five times per year and that it should recover quickly. This focuses on system reliability and recovery.

Identifying Insufficiencies

The insufficiency here is the lack of specific criteria. The phrase 'crash more than 5 times' is not specific enough, as it does not consider the severity or impact of each crash. Also, 'recover...as quickly as possible' is vague, providing no concrete time frame or steps for recovery.

Incorporating Specificity for Crashes

Amend the requirement to specify the extent or impact of each crash. For example, 'The system shall not suffer a critical crash more than twice per year, and no minor issues more than 5 times per year.' This separates the types and frequencies of possible failures.

Specifying Recovery Expectations

Define what 'quickly as possible' means in terms of recovery. Amend the requirement to include a clear recovery time objective such as, 'The system must recover within 30 minutes for major crashes and 10 minutes for minor issues.' This provides measurable expectations for system recovery.

Conclusion and Revised Requirement

A more effective requirement might be: 'The order entry system shall not suffer critical crashes more than twice per year and minor issues no more than 5 times annually. For major crashes, the system must recover within 30 minutes and for minor issues, within 10 minutes, to minimize downtime.' This version provides clear targets and definitions.

Key concepts

System Reliability

System reliability is a critical component of software requirements. It refers to the ability of a system to perform its intended function without failure under designated conditions for a specified period of time.
Reliability is important because it ensures that the system can handle required operations smoothly and consistently, minimizing unexpected downtime.
To improve reliability in an order entry system, it's essential to specify the parameters of what constitutes a "crash."
Without this delineation, it's challenging to measure reliability accurately, resulting in potential frustration for users and unclear performance standards for developers.
Incorporating measures such as specifying the number of acceptable critical and minor crashes helps enhance the understanding and handling of system reliability.

Recovery Time Objectives

Recovery time objectives (RTOs) are a key aspect of business continuity planning. They define the maximum allowable time for system recovery to minimize downtime after an incident.
This is crucial because it sets measurable and clear goals that guide the development and maintenance teams in prioritizing system recovery processes.
For instance, having an RTO of 30 minutes for critical crashes compels the team to focus on efficient recovery strategies to meet this specific timeframe. In contrast, vague terms like 'as quickly as possible' do not provide concrete targets, making it difficult to gauge whether recovery efforts are sufficient.
Thus, defining RTOs in terms of minutes or hours ensures clarity and facilitates consistent recovery outcomes.

Requirement Specificity

Requirement specificity is essential for creating clear, unambiguous expectations for system performance. Specificity reduces the risk of misinterpretation and provides a solid foundation for testing and verification processes.
When a requirement is too general or vague, such as stating a system should not crash or recover as soon as possible, it leads to varying interpretations and difficulties in achieving compliance.
To address this, requirements should detail the types and limits of acceptable failures, as well as the expected recovery time for each.
By including explicit metrics and definitions, software teams can create a more precise roadmap for achieving and verifying system objectives.

Impact Analysis

Impact analysis is the process of understanding the potential effects of system failures or changes to requirements on overall operations. It helps in identifying risks and dependencies, allowing teams to plan effectively for mitigation.
In the context of system reliability, impact analysis examines how different failure modes might affect business operations and what contingencies are required.
For example, understanding the impact of a system crash on order processing helps in setting realistic recovery time objectives and defining requirement specificity.
Through thorough impact analysis, stakeholders can prioritize areas in system development and maintenance, ensuring that critical functionalities are preserved and downtime is minimized. This analytical approach supports decision-making and enhances resilience.