ISBN: 9780201700640

There is a real and growing gap between the theory and practice of componentbased software design. There are, of course, books on componentbased design. However, these books assume that t… mais…

There is a real and growing gap between the theory and practice of componentbased software design. There are, of course, books on componentbased design. However, these books assume that the design task is to develop specifications for software components when most componentbased design relies on preexisting components. There is room for both perspectives. However, preexisting components introduce new and novel design challenges, and their use is becoming increasingly prominent. Preexisting components mean preexisting component specifications, and these are constraints onnot artifacts ofa design. Current componentbased design methods are focused on the less interesting and less encountered design problem. The more common and more interesting aspects of the design process are those that are no longer under the control of the designer. Use of preexisting components involves a completely different class of design problem than arises from component specification. Preexisting components involve the designer in selection decisions, while the freedom to define component interfaces involves the designer in optimization decisions. The difference between these classes of design problem are only gradually becoming evident to software engineers, and design methods have not yet caught up with this growing awareness. Use of preexisting components involves a significant loss of control over fundamental design decisions: how a system is partitioned into components, what functionality is provided by components, and how components coordinate their activities. In software engineering theory, these are architectural (that is, design) decisions. This leads to the mistaken conclusion that aggressive use of preexisting components is antithetical to, or at least incompatible or disjunctive with, software design. We have described briefly the state of componentbased design methods today, but have not yet supported the assertion that there is a growing gap between the theory and practice of componentbased development. In fact, the gap does exist and is selfevident, once you know where to look for it. The trend toward componentbased development has been well under way for more than fifteen years, and has its roots in the commercial software marketplace. Software products, such as relational database management systems, transaction monitors, message brokers, event managers, encryption services, Web browsers and servers, geographic information systems, product data management systems, ad infinitum, all satisfy the essential criteria of software component, at least as this term is coming to be understood by industry. That is, they all are implementations of functionality, are in binary form, are independently deployed, are described by a programmatic interface, and support thirdparty integration. The commercial marketplace is the primary source of software components. This is true today, and will remain so for the indefinite future. Indeed, we believe that components and the software component marketplace are inextricably linked. Szyperski, in his influential book, shares this belief by observing that a component must be defined to fill a market niche. However, Szyperski’s notion of market was largely (although not completely) metaphorical. In contrast, our use of the term component market refers to something that demonstrably exists today, complete with component suppliers, component infrastructure providers, thirdparty component integrators, and, ultimately, consumers. Ignoring the effects of the marketplace on software engineering would be analogous to ignoring the effects of friction on mechanical engineering. In particular, there are three qualities of commercial software components that together account for a significant share of the challenges posed by software components. Commercial software components are complex. This complexity is needed to justify and sustain a component market. Many components are sufficiently complex that even experts in their use do not know all their features. There are invariably unknowns about component features and behavior. Commercial software components are idiosyncratic. Standards are useful, but innovative features attract consumers. This means component knowledge is vendorspecific, and integration difficulties arise due to mismatches among innovative (that is, nonstandard) features. Commercial software components are unstable. New features must be introduced to motivate upgrade, and are needed where competitors have copied successful features. Component knowledge has a short halflife, and | Building Systems from Commercial Components by Robert Peter S. Gordon Paperback | Indigo Chapters Books > Computers > Software > Development P10116, Robert Peter S. Gordon<

ISBN: 9780201700640

There is a real and growing gap between the theory and practice of componentbased software design. There are, of course, books on componentbased design. However, these books assume that t… mais…

There is a real and growing gap between the theory and practice of componentbased software design. There are, of course, books on componentbased design. However, these books assume that the design task is to develop specifications for software components when most componentbased design relies on preexisting components. There is room for both perspectives. However, preexisting components introduce new and novel design challenges, and their use is becoming increasingly prominent. Preexisting components mean preexisting component specifications, and these are constraints onnot artifacts ofa design. Current componentbased design methods are focused on the less interesting and less encountered design problem. The more common and more interesting aspects of the design process are those that are no longer under the control of the designer. Use of preexisting components involves a completely different class of design problem than arises from component specification. Preexisting components involve the designer in selection decisions, while the freedom to define component interfaces involves the designer in optimization decisions. The difference between these classes of design problem are only gradually becoming evident to software engineers, and design methods have not yet caught up with this growing awareness. Use of preexisting components involves a significant loss of control over fundamental design decisions: how a system is partitioned into components, what functionality is provided by components, and how components coordinate their activities. In software engineering theory, these are architectural (that is, design) decisions. This leads to the mistaken conclusion that aggressive use of preexisting components is antithetical to, or at least incompatible or disjunctive with, software design. We have described briefly the state of componentbased design methods today, but have not yet supported the assertion that there is a growing gap between the theory and practice of componentbased development. In fact, the gap does exist and is selfevident, once you know where to look for it. The trend toward componentbased development has been well under way for more than fifteen years, and has its roots in the commercial software marketplace. Software products, such as relational database management systems, transaction monitors, message brokers, event managers, encryption services, Web browsers and servers, geographic information systems, product data management systems, ad infinitum, all satisfy the essential criteria of software component, at least as this term is coming to be understood by industry. That is, they all are implementations of functionality, are in binary form, are independently deployed, are described by a programmatic interface, and support thirdparty integration. The commercial marketplace is the primary source of software components. This is true today, and will remain so for the indefinite future. Indeed, we believe that components and the software component marketplace are inextricably linked. Szyperski, in his influential book, shares this belief by observing that a component must be defined to fill a market niche. However, Szyperskiâ??s notion of market was largely (although not completely) metaphorical. In contrast, our use of the term component market refers to something that demonstrably exists today, complete with component suppliers, component infrastructure providers, thirdparty component integrators, and, ultimately, consumers. Ignoring the effects of the marketplace on software engineering would be analogous to ignoring the effects of friction on mechanical engineering. In particular, there are three qualities of commercial software components that together account for a significant share of the challenges posed by software components. Commercial software components are complex. This complexity is needed to justify and sustain a component market. Many components are sufficiently complex that even experts in their use do not know all their features. There are invariably unknowns about component features and behavior. Commercial software components are idiosyncratic. Standards are useful, but innovative features attract consumers. This means component knowledge is vendorspecific, and integration difficulties arise due to mismatches among innovative (that is, nonstandard) features. Commercial software components are unstable. New features must be introduced to motivate upgrade, and are needed where competitors have copied successful features. Component knowledge has a short halflife, and | Building Systems from Commercial Components by Kurt Wallnau Paperback | Indigo Chapters Books > Computers > Software > Development P10116, Kurt Wallnau<