Appropriate software engineering-based supporting tools and environments should be available. Ada 83 tool sets must be modified somewhat for Ada 95 use, but Ada 95 versions are already available.
In this section, Ada 95 is rated with respect to the language characteristics used in Table 2 in the main document [ANSI/ISO 95] [Barnes 94]. The ratings range from 0 to 10, where 0 means the language provides no support for the characteristic, and 10 means it provides extensive support. The ratings given below are those provided in Table 2. The reader must bear in mind that the support for a good characteristic in a language does not necessarily mean that it is always used, or used appropriately. Unskilled programmers can write bad code in any language, but a good language facilitates the production of good code by skilled programmers.
Clarity of source code – the extent to which inherent language features support source code that is readable and understandable and that clearly reflects the underlying logical structure of the program.
Ada is considered by many to be very verbose, but one of the strengths of this language approach is that it supports code clarity. Ada code also reflects program structure. Clarity of form was one of the design goals of Ada. Rating: 9
Complexity management (architecture support) – the extent to which inherent language features support the management of system complexity, in terms of addressing issues of data, algorithm, interface, and architectural complexity.
The single most important contribution of Ada 83 to language design was the package construct. This construct permits the encapsulation of abstract data types, finite state machines, classes, objects, etc. Ada 95 has gone beyond this to provide additional support for managing the complexity of very large software components with hierarchical libraries. It also provides partitions for distributed systems. Rating: 9
Concurrency support – the extent to which inherent language features support the construction of code with multiple threads of control (also known as parallel processing).
Ada is one of few standardized languages with specific concurrency support. Ada 95 has improved concurrency support over Ada 83, and it has also introduced a Real-Time Systems Annex. This has better specified the required implementation of a useful model of concurrency. Rating: 8
Distributed system support – the extent to which inherent language features support the construction of code to be distributed across multiple platforms on a network.
Ada 95 provides specific support for distributed systems through the Distributed Systems Annex. Rating: 5
Maintainability – the extent to which inherent language features support the construction of code that can be readily modified to satisfy new requirements or to correct deficiencies.
Many features of Ada support maintainability, such as those which support code clarity and encapsulation, to facilitate understanding followed by the ability to change isolated pieces of code while guaranteeing no side effects in other parts of the software system. Ada 95 also has hierarchical libraries. The full object-oriented capabilities can have both good and bad effects on maintainability, but, if used properly, object-oriented programming will improve maintainability. Rating: 9
Mixed language support – the extent to which inherent language features support interfacing to other languages.
Ada 95 has a standardized interface mechanism and provides an Interface to Other Languages Annex. Rating: 8
Object-oriented programming support – the extent to which inherent language features support the construction of object-oriented code.
Ada 95 provides complete support for all aspects of a language generally recognized as making it object-oriented—encapsulation of objects and their operations, inheritance, and polymorphism. Ada 95 also provides support for other programming paradigms, so an individual Ada 95 program will not necessarily be object-oriented. Rating 10
Portability – the extent to which inherent language features support the transfer of a program from one hardware and/or software platform to another.
Ada features, such as the type attributes, the ability to define numerical types using system independent range and digits declarations, and the ability to encapsulate dependencies, provide good support for portability. Rating: 8
Real-time support – the extent to which inherent language features support the construction of real-time systems.
Ada features provide support for specifying time and space constraints. Ada 95 has a Real-Time Systems Annex that specifies the language definition for the implementation of real-time features. Rating: 7
Reliability – the extent to which inherent language features support the construction of components that can be expected to perform their intended functions in a satisfactory manner throughout the expected lifetime of the product.
Ada requires the specification of information, the omission of which can make a program unreliable, such as type specifications. Ada also performs consistency checks across separately compiled units, providing excellent support for reliability. Rating: 9
Reusability – the extent to which inherent language features support the adaptation of code for use in another application.
Ada supports reusability with language features supporting code clarity (making code understandable), encapsulation (making code adaptable), maintainability, and portability. Ada 95 also supports object-oriented programming and hierarchical libraries. Rating: 8
Safety – the extent to which inherent language features support the construction of safety-critical systems, yielding systems that are fault-tolerant, fail-safe, or robust in the face of systemic failures.
As noted by [Pyle 91] and [Cullyer 91], no language alone can ensure the construction of safety-critical systems (additional formal methods are required). However, Ada comes closer than other existing languages by an order of magnitude because of its support for system reliability [Pyle 91]. Ada 95 has a Safety and Security Annex. Rating: 6
Standardization – the extent to which the language definition has been formally standardized (by recognized bodies such as ANSI and ISO) and the extent to which it can be reasonably expected that this standard will be followed in a language translator.
Ada 95 has been standardized by ANSI and ISO in a much different fashion than other languages, with compilers developed after the language was standardized. The expectation is that every Ada 95 compiler will be validated against the standard, and the compilers will follow the standard without adding non-standard features to the language definition, just as is the case with Ada 83. Rating: 10
Support for modern engineering methods – the extent to which inherent language features support the expression of source code that enforces good software engineering principles.
Ada requirements were developed explicitly to support good software engineering. Rating: 9