Checklist: Architecture |
This checklist provides questions to help in evaluating whether architectural decisions have been captured appropriately.
Relationships
Related Elements | Architecture
Check Items
General
In general, the architecture must support the needs of the development team for the current iteration: Does the architecture appear to be stabilizing? Although the architecture may be unstable during early Inception and Elaboration iterations, it should become more stable toward the end of Elaboration, with sufficient stability during Construction to allow the team to build the software efficiently and with confidence. The architecture should be very stable during the Transition phase. Does the architecture divide the system’s responsibilities into well-defined subsystems with well-defined interfaces? Are all of the subsystem components for the iteration identified? Are the number and types of components reasonable? Does the packaging approach reduce complexity and improve understanding? Are packages defined to be highly cohesive within the package, while the packages themselves are loosely coupled? Can team members understand enough from the architecture to successfully design and code their allocated components? Is the architecture description current? Have the design guidelines been followed? Are all technical risks either mitigated or addressed in a contingency plan? Does the architecture address all of the non-behavioral requirements in the Supplementary Requirements? If not, is there a plan to address them?
Architecture Qualities
The architectural qualities are specified, with appropriate Architectural Mechanism in place to meet them. For example: Error recovery For each error or exception, a policy defines how the system is restored to a normal state. For each possible type of user-input error incorrect data from external systems, written procedures explain how to restore the system normal state. There is a consistently applied policy for handling exceptional situations. There is a consistently applied policy for handling data corruption in the database. There is a consistently applied policy for handling database unavailability, including whether data can still be entered into the system and stored later. If data is exchanged between systems, there is a policy for how systems synchronize their views of the data. If the system uses redundant processors or nodes to provide fault tolerance or high availability, there is a strategy for ensuring that no two processors or nodes act on the assumption that they are primary and that no processor or node is primary. The failure modes for a distributed system have been identified and strategies defined for handling the failures. Performance Performance requirements are reasonable and reflect real constraints in the problem domain; their specification is not arbitrary. Estimates of system performance exist (using a Workload Analysis Model as necessary), and these indicate that the performance requirements are not significant risks. System performance estimates have been validated using architectural prototypes, especially for performance-critical requirements. Memory use Memory budgets for the application have been defined. Actions have been taken to detect and prevent memory leaks. There is a consistently applied policy that defines how the virtual memory system is used, monitored, and tuned. Portability Portability requirements have been met. Programming Guidelines provide specific guidance for creating portable code. Design Guidelines provide specific guidance for designing portable applications. A test port has been created to verify portability claims. Reliability Measures of quality (MTBF, number of outstanding defects, and so on) have been met. The architecture provides for recovery in the event of disaster or system failure Security Security requirements have been met.
Architecture Description
#### The Use-Case View For the Use-Case View section of the Software Architecture document: Is each architecturally significant Use Case identified as such for these reasons: Is vitally important to the stakeholders? Motivates key elements in the other views? Is a driver for mitigating one or more major risks, including any challenging non-functional requirements? Are there any Use Cases whose architectural concerns are already covered by another Use Case? Are the architecturally significant aspects of the Use Case clear, not lost in details? Are the Use Cases sufficiently clear and unlikely to change in a way that affects the architecture, or is there a plan in place for how to achieve such clarity and stability? Have any architecturally significant Use Cases been missed? Note: This may require analysis of the Use Cases not selected for this view. Can the architecture handle all Use Case realizations defined for the current iteration? #### The Logical View For the Logical View section of the Software Architecture document: Does it accurately and completely present an overview of the architecturally significant elements of the design? Does it present the complete set of architectural mechanisms used in the design, along with the rationale for their selection? Does it present the layering of the design, along with the rationale used to partition the layers? Does it present any frameworks or patterns used in the design, along with the rationale for selecting those patterns or frameworks? #### The Process View For the Process View section of the Software Architecture document: Are potential race conditions (process competition for critical resources) identified, and have you defined avoidance and resolution strategies? Are the nominal and maximal performance requirements for important operations specified? Is there is a set of performance tests capable of measuring whether performance requirements have been met? Have any architectural weaknesses with the potential for performance bottlenecks been identified? Is there consistent policy for handling errors and exceptions in the system? Is the system tolerant of errors and exceptions, so that when an error or exception occurs, the system can revert to a consistent state? #### The Deployment View For the Deployment View section of the Software Architecture document: Does the deployment conform to all Stakeholder’s deployment requirements? Have the system availability requirements been addressed? Have the system capacity requirements been addressed?
Models
#### Overall Subsystem and package partitioning and layering is logically consistent. All analysis mechanisms have been identified and described. #### Subsystems The services (interfaces) of subsystems in upper-level layers have been defined. The dependencies between subsystems and packages correspond to dependency relationships between the contained classes. The classes in a subsystem support the services identified for the subsystem. #### Classes The key entity classes and their relationships have been identified. Relationships between key entity classes have been defined. The name and description of each class clearly reflects the role it plays. The description of each class accurately captures the responsibilities of the class. The entity classes are mapped to analysis mechanisms, where appropriate. The role names of aggregations and associations accurately describe the relationships between the related classes. The multiplicities of the relationships are correct. The key entity classes and their relationships are consistent with the business model (if it exists), domain model (if it exists), requirements, and glossary entries. #### General Model Considerations The model is at an appropriate level of detail, given the model objectives. For the business, requirements, or design models during the Elaboration phase, there is not an over-emphasis on implementation issues. For the design model in the Construction phase, there is a good balance of functionality across the model elements, and it combines relatively simple elements to build a more complex design. The model demonstrates familiarity and competence with the full breadth of modeling concepts applicable to the problem domain; modeling techniques are used appropriately for the problem at hand. Concepts are modeled in the simplest way possible. The model can easily evolve, and expected changes can be easily accommodated. At the same time, the model has not been overly structured to handle unlikely change at the expense of simplicity and comprehensibility. The key assumptions that the model is based on are documented and visible to reviewers of the model. If the assumptions are applicable to a given iteration, then the model should be able to evolve within those assumptions, but not necessarily outside of those assumptions. Documenting assumptions is a way of indemnifying designers from not being expected to consider all possible requirements. In an iterative process, it is impossible to analyze all possible requirements and to define a model that will handle every future requirement.
Transition and Installation
The process for upgrading an existing system without loss of data or operational capability is defined and has been tested. The process for converting data used by previous releases is defined and has been tested. The amount of time and resources required to upgrade or install the product is well-understood and documented. The functionality of the system can be activated one Use Case at a time.
Administration
Disk space can be reorganized or recovered while the system is running. The responsibilities and procedures for system configuration have been identified and documented. Access to the operating system or administration functions is restricted. Licensing requirements are satisfied. Diagnostics routines can be run while the system is running. The system monitors operational performance (capacity threshold, critical performance threshold, resource exhaustion). The actions taken when thresholds are reached are defined. The alarm-handling policy is defined. The alarm-handling mechanism is defined and has been prototyped and tested. The alarm-handling mechanism can be adjusted to prevent false or redundant alarms. The policies and procedures for monitoring and administration the network (LAN, WAN) are defined. Faults on the network can be isolated. There is an event-tracing mechanism that can be enabled to aid in troubleshooting. The overhead of the facility is understood. The administrative staff possesses the knowledge to use the facility effectively. It is not possible for a malicious user to: Enter the system Destroy critical data Consume all resources
Organizational Issues
By the completion of the Elaboration phase, the architecture should be sufficiently well-defined to allow decisions about the structure of the team: Does the component architecture provide a suitable basis for organizing the development teams? Does each team have the skills required to implement their allocated components? Are responsibilities divided well between teams? Do all team members share the same understanding of the architecture as the one presented by the architect?
Cost and Schedule
The actual number of lines of code developed thus far matches the estimated lines of code at the current milestone. The estimation of cost and schedule assumptions have been reviewed and remain valid. Cost and schedule estimates have been recalculated using the most recent actual project experience and performance.
More Information
Concepts | Architectural Mechanism
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