Chapter 2
Why Adopt Ada 95?

• Summary of Adoption Issues
• What is Ada 95?
  • Ada 95 Builds Incrementally on Ada 83
• Why Was Ada 95 Developed?
• Why Use Ada 95 Over Ada 83?
  • Features and Benefits of Ada 95
  • Increase Functionality
  • Faster Development of Systems
• Why Use Ada 95 Rather Than Language X?
  • Ada 95 Provides New and Unique Features
  • Moving from Procedural Languages: FORTRAN, C, COBOL, JOVIAL, CMS-2, etc.
  • Choosing among Object-Oriented Languages: Ada 95, C++, Smalltalk, etc.
  • Using with 4GLs: DBase, Focus, etc.
• Trial Ada 95 Technology Available
• Stability of the Ada 95 Definition
• DOD's Policy on Ada 95
• Early Results of Using Ada 95
• Support for Migration Systems and Multi-Language Development
• Conclusions

Summary Of Adoption Issues

PEOs and PMs now have the opportunity to adopt Ada 95. This chapter provides a rationale for why they may want to take advantage of Ada 95 features and benefits. As noted in the Introduction, subsequent chapters will address the risks associated with Ada 95 adoption and provide risk mitigation strategies. Each subsection in this chapter describes the reasons why PEOs and PMs would consider adopting Ada 95 from both the perspective of those using Ada 83 and those using other languages. Tables 1 and 2 summarize the key management and technical benefits that Ada 95 may provide.

Table 1: Key Management Benefits in the Switch to Ada 95

Table 2: Key Technology Reasons to Switch to Ada 95

What is Ada 95?

Ada 95 is the informal name for the current Ada standard (ISO/IEC 8652:1995). It is an incremental improvement of the Ada 83 (ANSI/MIL-STD-1815A) programming language. It is neither a new language nor some radical redesign. When moving to Ada 95, you keep your Ada 83 software and your investment in Ada 83 training, tools, or technology. The transition is a natural evolution. As Figure 1 shows, the new language overcomes some limitations of Ada 83 and adds new features to the existing Ada 83 language.

Ada 95 Builds Incrementally on Ada 83

Ada 83 developers can build on their existing knowledge when learning Ada 95. The new parts of the language can be learned gradually and its benefits incorporated in small steps. Immediate benefits are realized by beginning to use Ada 95's simpler features while building up to using all the features that the language has to offer. This enables the developers to follow the KISS principle. While an incremental approach simplifies learning and lowers costs, development teams may not realize all the benefits immediately.



Figure 1: The Incremental Nature of Ada 95 - Ada 83 Plus Enhancements

Why Was Ada 95 Developed?

So, why is here an Ada 95? One reason is that users demanded it. Programming technology advances rapidly -- many technologies have matured since 1983, including object-oriented programming, client/server and distributed computing, and improved real-time scheduling algorithms -- just to name a few. Like most software users, Ada's customers demanded both new features and improvements to existing ones. Feedback from the users of Ada 83 was positive; their projects were successful. But people wanted features that weren't available in Ada 83.

ANSI standards must be reviewed every five years. The Ada Board, based on its perception that there were things that should be changed and added to Ada 83, recommended that the standard be revised. When the Ada revision process started in 1988, users around the world sent in more than 750 revision requests. The language revision was an open, publicly reviewed process. This consensus-based approach included involving users who reviewed and commented on the changes to the language at workshops, conferences, through the Internet and, of course, as part of the formal standards committee.

Why Use Ada 95 Over Ada 83?

Ada 95 is the next version upgrade to the language. Table 3 summarizes the management benefits of the major new technical features available in Ada 95. If your system has the properties shown in the first column of the table ("Systems That Have These Characteristics"), then you are likely to benefit from Ada 95.

Features and Benefits of Ada 95

Management reasons to switch to Ada 95 include:
• Lower Costs through Software Reuse - Object-oriented programming and interfacing features of Ada 95 will support large-scale reuse (i.e., use of existing class libraries, etc.).

• More Efficient Development - New hierarchical libraries will reduce the amount of recompilation needed to develop and maintain large software systems, thus accelerating development and making your software workforce more productive.

• More Efficient Software - Several new, more efficient concurrency features will enhance real-time performance.

• Improved Maintainability - Both object-oriented programming and hierarchical libraries will make software changes to meet new user requirements quicker and more efficient.

• Eventual Loss of Ada 83 Support - Vendors will be targeting the majority of their resources to support the new versions of Ada compilers. Although support for both Ada 83 and Ada 95 will be available for a period of time, eventually only Ada 95 will be supported.

Increased Functionality

Ada 95 makes available new language features not found in Ada 83. Table 3 summarizes their benefits. These features are grouped into four major categories:
• Object-Oriented Programming (OOP) - The ability to develop new software components by specifying how they are similar to and different from existing components. OOP is a popular approach to help make software easier to modify and less costly to build and maintain.

• Hierarchical Library Units: Increased Support for Programming-in- the-Large - The ability to structure large packages into groups of small related "subsystems" that are more understandable, can compile and recompile faster, and can decrease executable code size. The hierarchical library units result in software that can be modified more easily, greater developer productivity, and lower cost.

• Real-Time Enhancements - New real-time constructs (e.g., protected types) provide more efficient support for data-oriented concurrency. More direct support for interrupting processing to respond to mode changes is provided. These real-time features decrease the risk of using Ada over assembly languages. Real-time enhancements also increase software efficiency.

• Interfacing with Other Software - Better and more intimate interoperation with COTS and GOTS software written in other languages. This interfacing feature increases software interoperability.

• Specialized Needs Annexes - The annexes define support for many domains. Packages to help support legacy applications in information systems. An annex providing a portable model for producing distributed Ada programs supports client/server computing and distributed computing. Real-time systems are supported by packages and commands to provide more sophisticated scheduling and concurrency needs. Additionally, auxiliary libraries support areas such as formatted IO and advanced math functions. Specialized needs annexes allow vendors to provide greater amounts of specialized support to their customers within the standard.

Faster Development of Systems

New Ada 95 features will allow programmers to be significantly more productive than their Ada 83 counterparts. Ada 95 adds new capabilities and rules to Ada to reduce the amount of recompilation. Large Ada 83 projects will benefit from the ability of users to modify their system by extending existing software rather than by changing its interface (interface changes have caused extra recompilation time for large Ada 83 systems). Programmers primarily exploit extensibility in Ada 95 through the use of child library units (to extend existing packages with new functionality), and through inheritance (to extend types with new values and operations/functionality). Both features extend the software without recompiling the parts of the system that depend only on the parent package. The enhanced generic capability in Ada 95 allows developers to build templates and then change their implementation without impacting users of those templates.

Table 3: Benefits of Using the New Features of Ada 95 in Various Systems

Why Use Ada 95 Rather Than Language X?

Once an organization has decided to consider a language change, several issues must be considered. Typically, an organization will move from its existing language to another language when the benefits of the new language clearly outweigh the effort to change the status quo (e.g., training, buying new tools, etc.). The following subsections describe some of the advantages and the disadvantages Ada 95 has, compared with other programming languages. Individually, many of these features are not unique to Ada 95, but taken together, they make Ada 95 a good alternative to other languages.

Ada 95 Provides New and Unique Features

Ada 95 will keep developers competitive. Ada 95 provides the same kinds of features found in other modern languages. These include: support for object-oriented programming, strong real-time building blocks, and the ability to more directly access the hardware system. All these features supplement the features of Ada 83: packages and generics (promoting reuse and modifiability), tasking directly integrated into the language (supporting concurrency and real-time programming), exception handling (promoting safety and reliability), and a rich set of built-in structures and types (making the software reflect the real world).

Choosing Ada 95 keeps development efforts abreast of Industry. Ada 95's developers have taken lessons from the best Object-Oriented Programming Languages (OOPLs) to ensure that it will be a language for the 20th and the 21st centuries. Ada 95 doesn't just provide technical parity with other languages, in some ways it surpasses them. Ada 95 provides a rich set of OOP features and integrates them with tasking and generics. Table 4 compares features found in C++ and Smalltalk with those in Ada 95. Ada 95 provides the power of object-oriented programming - reuse, higher productivity and lower maintenance costs.

Table 4: Comparison of the OOP Features of Ada 95 and Other Popular OOPLs



Using a high-level language, for real-time applications, decreases technical risks, provides increased productivity, lower cost and greater system reliability. Ada 95 provides enhanced support for embedded weapons systems and other real-time projects. New real-time features include a more efficient language primitive for providing exclusive access to shared data (protected types), more flexible ways to respond to a mode change or interrupt (the new "select with" abort ), and more flexible scheduling of tasks. These features enable the use of Ada 95 where assembly language or low-level languages were previously used, thus providing increased productivity and reliability while lowering cost. It also supports PEOs and PMs in the move from specialized hardware platforms (e.g., UYK-43 and UYK-44) to open systems (e.g., commercial platforms using POSIX, etc.).

Ada's unique features include special support for many common application domains. Ada 95 provides several "specialized needs annexes", which define additional libraries and support for particular domains such as real-time, numerical, distributed, and information systems. These capabilities will make Ada 95 the first distributed, concurrent, object-oriented programming language to become an international standard. These specialized needs annexes will increase portability for applications within specific domains by ensuring standard interfaces to needed services. However, projects will only achieve this when they use compilers that support those annexes. For maximum portability, projects should use only the features found in the core of Ada 95.

Standard interfaces to other languages are included so that Ada programs may make use of existing code written in C, COBOL, and FORTRAN. In fact, Ada 95 is intended to exist cooperatively in a multi-language environment; this makes it suitable for migrating and re-engineering legacy systems so groups can continue to use the old system as a part of the new effort. Finally, standard Ada 83 bindings exist that permit Ada to be used with SQL. Ada 95 bindings to SQL-2 are under development.

Moving from Procedural Languages: FORTRAN, C, COBOL, JOVIAL, CMS-2, etc.

Ada 95 provides all the benefits of Ada 83 - a 10-year track record of higher productivity, lower maintenance costs, and lower technical risks because Ada 83 is the core of Ada 95.

Ada 95 is also an opportunity to adopt modern methods and processes. PEOs and PMs are migrating their organizations and re-engineering their legacy systems. These migration efforts offer an opportunity to introduce more modern software engineering technology. Migration and re-engineering efforts allow the PEO and PM an opportunity to adopt a newer programming language. Ada 95 is an important option -- it brings with it the ability for an organization to improve its entire software development process. Both events can have a synergistic effect.

Adopting Ada 95 lowers the project's risks because Ada 95 provides the improvements of other modern languages - with some significant differences. Once PEOs or PMs have decided to move from their existing procedural language, the choice is then, to what new language? If the move stems from a desire to adopt an OOPL, then Ada 95 is a good choice compared with other current alternatives: it possesses a richer set of features than Smalltalk; and it is simpler to understand, read, and maintain than C++. Its facilities for real-time support are unparalleled in any other standardized language. All these benefits are part of an ANSI and ISO standardized language. In addition, Ada represents a DOD core competency - DOD has the skills, tools, and infrastructure to support Ada. When PEOs and PMs consider changing from procedural programming languages, Ada 95 is the low-risk alternative.

Choosing among Object-Oriented Languages: Ada 95, C++, Smalltalk, etc.

Ada 95 builds upon the lessons learned from other OOPLs; therefore, it lowers the risk PEOs and PMs take when adopting a new programming language. With the large numbers of OOPLs that have emerged in the past few years, choosing the right one can be difficult. In addition to evaluating the technical merits of the language (see Table 4), managers should be aware of other impacts of choosing a language such as:
• Vendor Independence (through use of a standardized language) - Ada 95 will become an international standard ahead of all other OOPLs; this ensures that all compilers, from all vendors, will provide the same language facilities. Projects making use of only core Ada 95 features will find this to be true for all compilers. Those making use of features from the annexes will find it true for those compilers that support those annexes. Standardization enhances portability - there are fewer incompatibilities when moving from Vendor A's Ada to Vendor B's.

• Lower Development Cost and Maintenance Cost - PEOs must consider the trade-off of development costs now versus maintenance costs later. Ada 95 provides balanced support to both a fast time to market (through Ada's large set of standard libraries and good reuse support), and long-lived projects (common standards to lower maintenance costs and a common language to facilitate a pool of skilled software engineers). In balancing these demands, Ada 95 is as strong as C++. It does not try to replace rapid prototyping technology, however. These reuse benefits accrue to projects that use existing components. PEOs and PMs should remember that projects that create reusable components are making an investment and must be prepared for that extra cost. Ada 95's features, such as high readability and hierarchical library units, supplement Ada's OOP features in supporting both quick time to market and lower maintenance costs.

• Ability to Trade Performance for Power/Productivity - Ada 95 is based on the philosophy of providing developers with building blocks. This enables them to know the costs associated with any language features they use. Ada 95 was designed to enable the technical staff to use the right tool for the right job.

• Acceptable Training Costs - Training costs are related to the time required to learn and use the language. Ada 95 is more expressive (powerful) than many OOPLs and also provides this expressive power in ways that may make learning Ada 95 no more difficult than learning C++. Although there is only limited experience through tutorials and industry classes, early Ada 95 training costs seem comparable to those of other languages.

See Table 4 for a detailed comparison of the features found in Ada 95, C++, and Smalltalk.

Using with 4GLs: DBase, Focus, etc.

Ada 95 co-exists with and supplements 4GLs, allowing PEOs and PMs to gain the power of both technologies and lowering the risk for information systems to move to Ada 95. There are some instances when a project may want to choose a procedural 3GL, such as Ada 95, over a non-procedural 4GL, especially when the 4GL doesn't provide enough functionality to supply special, application-specific behaviors. In this case, Ada 95 may either replace the use of a 4GL or be used to implement application-specific routines that are called from the generated 4GL code (e.g., actions when a user presses a button on a graphical user interface [GUI] screen). In other applications, Ada 95 could be used jointly with 4GLs -- especially since Ada 95 has added new features that allow it to be called by other programming languages as well as call on them. One common strategy will be to use the 4GL for the GUI and database access components and have Ada 95 code serve as the application specific functionality.

Trial Ada 95 Technology Available

Low-risk, low-cost options are available to introduce Ada 95 into a project. Inexpensive sources of Ada 95 technology are available, allowing the PEO or PM the opportunity to try the technology before undertaking full-scale adoption. Appendix A lists a number of ways to get information and products including: a free compiler for Ada 95, called GNAT, which is useful for training and pilot project efforts; free software components; and example programs, booklets, articles and tutorials. The availability of this technology lowers the cost of evaluating and adopting Ada 95, compared to Ada 83's costs. Team members will be able to find out quickly and easily about the new Ada 95 features and see how to apply them.

Development teams can assess the cost/benefit trade-off for each new feature and use only those that benefit their project. Teams will not pay a cost for Ada 95 features they don't use. Users may adopt Ada 95 incrementally, using only a few of the new features at one time. The language designers made sure that systems that don't use a new Ada 95 feature will not suffer any performance cost (either size or speed). This means that a new feature will affect a development effort only if it is used. For example, if a project does not make use of OOP features, then the project will not suffer any execution time penalty in speed or size.

Stability of the Ada 95 Definition

The international standardization of Ada 95 has produced careful language scrutiny and review, which ensures that the language definition is stable and mature. This means lower risk for projects adopting Ada 95. In addition, the presence of an international standard increases portability and supports DOD's efforts to make use of commercial standards.

Ada 95 became the first internationally standardized object-oriented programming language on February 15, 1995. It has been sanctioned as meeting FIPS standard 119-1 and is undergoing ANSI standardization. There will be no DOD specific Standard. This supports DOD's quest to move toward greater use of commercial standards maintained by outside standards bodies. It also makes Ada 95 more attractive to commercial firms. Ada 95 is a stable, international standard that will provide PEOs and PMs with lower risk on their projects.

DOD's Policy on Ada 95

Ada 95 is the current version of Ada. Therefore, no special permission is needed to use Ada 95.

In addition, Emmett Paige, Jr., the Assistant Secretary of Defense for Command, Control, Communications and Intelligence [ASD(C3I)] has issued a memo, Figure 2, encouraging the early adoption and use of Ada 95.

The DOD policy on Ada 95 will allow the use of either Ada 83 or Ada 95 for a transition period. After that transition period, Ada 95 usage will be required. This approach parallels the way tool vendors support new versions of their products and phase out support for the older versions over time.

Figure 2: Early Use of Ada 95 Memorandum

Early Results of Using Ada 95

Partial Ada 95 implementations have been used during the language definition. Their lessons learned have reduced the risk for projects now adopting Ada 95. During the process of defining Ada 95, the language revision team worked with three User/Implementor teams to prototype Ada 95 technology and verify that the language would work as envisioned. These teams built partial Ada 95 compilers and used them on pilot projects to test the new language features. Early results were encouraging. In the area of real-time systems, the teams found that Ada 95 concurrency features yield large efficiency gains over using Ada 83 tasking. In the OOP area, the early users found that they gained the promised benefits of reuse and productivity, with surprisingly low overhead.

PEOs and PMs should remember, however, that these were early results with partial compilers. It remains to be seen whether the complete implementations of the standard language work better, the same, or not as well in these and other areas.

In addition to these teams, production projects have begun using Ada 95. Among these early adopters is the Patriot Fire Control system, which is re-engineering legacy assembly and JOVIAL code into Ada 95 software. The AJPO is supporting a number of technology transition partners in the early adoption of Ada 95. Drawn from all services, four major project efforts encompass the information systems, command and control, and embedded weapons systems domains. These projects include:

• The joint U.S. Air Force, U.S. Marine Corps and U.S. Navy project on Joint Applications Support Technology (JAST) - an embedded weapons system to support new aircraft.

• The U.S. Army's Common Applications Support System - a command and control support system. This is the common support system for the Army Tactical Command and Control System (ATCCS) project.

• DISA's Airfields project - a part of the Global Command and Control System (GCCS).

Support For Migration Systems and Multi-Language Development

Ada 95 reduces the risks to projects that must support multiple programming languages. Both cost and schedule will benefit by the improved ability to interface with legacy software, COTS, GOTS and other "class libraries" of reusable components -- those written in Ada and those written in other languages.

Many software projects of the 1990s are either migration systems efforts (which consolidate several systems into one) or re-engineering efforts (which take legacy code and obtain a more maintainable modern system while preserving the work invested in the legacy code). Both types of projects are similar because they require that the new code smoothly integrate with the existing legacy software. Multi-language development has always been a difficult task, but Ada 95 has several new features that make this simpler than it has been before.

As already noted, Ada 95 defines standard mechanisms for interfacing with other programming languages. In addition, the standard defines additional support packages to simplify interfacing with C, FORTRAN and COBOL. These support packages provide a portable, efficient and standard interface to legacy software. Built-in support from the language lowers the risk present in the new development effort and enhances characteristics such as portability. It also allows Ada 95 programs to use proven building blocks written in other languages as part of the Ada 95 application. This "peaceful coexistence" feature allows PEOs and PMs to make use of libraries of COTS or existing code. This reduces costs and speeds development.

PEOs and PMs should be aware that while the standard allows interfacing to any language, it does not require that all languages be supported by all compilers. Projects should be sure to evaluate each compiler's support for interfacing to their particular programming languages as a part of the compiler selection process.

Additionally, Ada 95 has the ability to be called by code written in other languages. This "call-in" capability allows Ada 95 code to be used to incrementally replace functionality present in a legacy system under maintenance, with minimal risk and disruption.

Conclusions

Whether moving from Ada 83 or from another language, Ada 95 can provide significant benefits to help PEOs and PMs minimize budget and schedule disruptions and other risks. Ada 95 adoption can help a software team to provide more capabilities for every dollar spent. However, to exploit these opportunities, the process of adopting Ada 95 - as with the adoption of any new technology - must be managed in order to minimize transition-related risks. The next chapters will help PEOs and PMs understand the adoption process, assess and manage the risks, and successfully transition to Ada 95 wherever it is appropriate and effective to do so.

Previous Chapter - Introduction

Next Chapter - Ada 95 Adoption Risks: Analysis and Mitigation

Table of Contents