物件導向軟體之架構(Object-Oriented Software Construction)探討

From the Book:
“Clean code that works” is Ron Jeffries’ pithy phrase. The goal is clean code that works, and for a whole bunch of reasons:
Clean code that works is a predictable way to develop. You know when you are finished, without having to worry about a long bug trail.Clean code that works gives you a chance to learn all the lessons that the code has to teach you. If you only ever slap together the first thing you think of, you never have time to think of a second, better, thing. Clean code that works improves the lives of users of our software.Clean code that works lets your teammates count on you, and you on them.Writing clean code that works feels good.But how do you get to clean code that works? Many forces drive you away from clean code, and even code that works. Without taking too much counsel of our fears, here’s what we do—drive development with automated tests, a style of development called “Test-Driven Development” (TDD for short). 
In Test-Driven Development, you:
Write new code only if you first have a failing automated test.Eliminate duplication.

Two simple rules, but they generate complex individual and group behavior. Some of the technical implications are:You must design organically, with running code providing feedback between decisionsYou must write your own tests, since you can’t wait twenty times a day for someone else to write a testYour development environment must provide rapid response to small changesYour designs must consist of many highly cohesive, loosely coupled components, just to make testing easy

The two rules imply an order to the tasks ofprogramming:
1. Red—write a little test that doesn’t work, perhaps doesn’t even compile at first
2. Green—make the test work quickly, committing whatever sins necessary in the process
3. Refactor—eliminate all the duplication created in just getting the test to work


Red/green/refactor. The TDD’s mantra.

Assuming for the moment that such a style is possible, it might be possible to dramatically reduce the defect density of code and make the subject of work crystal clear to all involved. If so, writing only code demanded by failing tests also has social implications:
If the defect density can be reduced enough, QA can shift from reactive to pro-active workIf the number of nasty surprises can be reduced enough, project managers can estimate accurately enough to involve real customers in daily developmentIf the topics of technical conversations can be made clear enough, programmers can work in minute-by-minute collaboration instead of daily or weekly collaborationAgain, if the defect density can be reduced enough, we can have shippable software with new functionality every day, leading to new business relationships with customers


So, the concept is simple, but what’s my motivation? Why would a programmer take on the additional work of writing automated tests? Why would a programmer work in tiny little steps when their mind is capable of great soaring swoops of design? Courage.
Courage
Test-driven development is a way of managing fear during programming. I don’t mean fear in a bad way, pow widdle prwogwammew needs a pacifiew, but fear in the legitimate, this-is-a-hard-problem-and-I-can’t-see-the-end-from-the-beginning sense. If pain is nature’s way of saying “Stop!”, fear is nature’s way of saying “Be careful.” Being careful is good, but fear has a host of other effects:
Makes you tentativeMakes you want to communicate lessMakes you shy from feedbackMakes you grumpy

None of these effects are helpful when programming, especially when programming something hard. So, how can you face a difficult situation and:
Instead of being tentative, begin learning concretely as quickly as possible.Instead of clamming up, communicate more clearly.Instead of avoiding feedback, search out helpful, concrete feedback.(You’ll have to work on grumpiness on your own.) 

Imagine programming as turning a crank to pull a bucket of water from a well. When the bucket is small, a free-spinning crank is fine. When the bucket is big and full of water, you’re going to get tired before the bucket is all the way up. You need a ratchet mechanism to enable you to rest between bouts of cranking. The heavier the bucket, the closer the teeth need to be on the ratchet.

The tests in test-driven development are the teeth of the ratchet. Once you get one test working, you know it is working, now and forever. You are one step closer to having everything working than you were when the test was broken. Now get the next one working, and the next, and the next. By analogy, the tougher the programming problem, the less ground should be covered by each test.

Readers of Extreme Programming Explained will notice a difference in tone between XP and TDD. TDD isn’t an absolute like Extreme Programming. XP says, “Here are things you must be able to do to be prepared to evolve further.” TDD is a little fuzzier. TDD is an awareness of the gap between decision and feedback during programming, and techniques to control that gap. “What if I do a paper design for a week, then test-drive the code? Is that TDD?” Sure, it’s TDD. You were aware of the gap between decision and feedback and you controlled the gap deliberately.

That said, most people who learn TDD find their programming practice changed for good. “Test Infected” is the phrase Erich Gamma coined to describe this shift. You might find yourself writing more tests earlier, and working in smaller steps than you ever dreamed would be sensible. On the other hand, some programmers learn TDD and go back to their earlier practices, reserving TDD for special occasions when ordinary programming isn’t making progress.

There are certainly programming tasks that can’t be driven solely by tests (or at least, not yet). Security software and concurrency, for example, are two topics where TDD is not sufficient to mechanically demonstrate that the goals of the software have been met. Security relies on essentially defect-free code, true, but also on human judgement about the methods used to secure the software. Subtle concurrency problems can’t be reliably duplicated by running the code.

Once you are finished reading this book, you should be ready to:
Start simplyWrite automated testsRefactor to add design decisions one at a time

This book is organized into three sections.
An example of writing typical model code using TDD. The example is one I got from Ward Cunningham years ago, and have used many times since, multi-currency arithmetic. In it you will learn to write tests before code and grow a design organically.An example of testing more complicated logic, including reflection and exceptions, by developing a framework for automated testing. This example also serves to introduce you to the xUnit architecture that is at the heart of many programmer-oriented testing tools. In the second example you will learn to work in even smaller steps than in the first example, including the kind of self-referential hooha beloved of computer scientists.Patterns for TDD. Included are patterns for the deciding what tests to write, how to write tests using xUnit, and a greatest hits selection of the design patterns and refactorings used in the examples.

I wrote the examples imagining a pair programming session. If you like looking at the map before wandering around, you may want to go straight to the patterns in Section 3 and use the examples as illustrations. If you prefer just wandering around and then looking at the map to see where you’ve been, try reading the examples through and refering to the patterns when you want more detail about a technique, then using the patterns as a reference.

Several reviewers have commented they got the most out of the examples when they started up a programming environment and entered the code and ran the tests as they read.

A note about the examples. Both examples, multi-currency calculation and a testing framework, appear simple. There are (and I have seen) complicated, ugly, messy ways of solving the same problems. I could have chosen one of those complicated, ugly, messy solutions to give the book an air of “reality.” However, my goal, and I hope your goal, is to write clean code that works. Before teeing off on the examples as being too simple, spend 15 seconds imagining a programming world in which all code was this clear and direct, where there were no complicated solutions, only apparently complicated problems begging for careful thought. TDD is a practice that can help you lead yourself to exactly that careful thought.

Test Driven Development: By Example

[서평]「Component Software」 - Beyond Object-Oriented Programming -

The new Semantic Web recommendations for RDF, RDFS and OWL have, at their heart, the RDF graph. Jena2, a second-generation RDF toolkit, is similarly centered on the RDF graph. RDFS and OWL reasoning are seen as graph-to-graph transforms, producing graphs of virtual triples. Rich APIs are provided. The Model API includes support for other aspects of the RDF recommendations, such as containers and reification. The Ontology API includes support for RDFS and OWL, including advanced OWL Full support. Jena includes the de facto reference RDF/XML parser, and provides RDF/XML output using the full range of the rich RDF/XML grammar. N3 I/O is supported. RDF graphs can be stored in-memory or in databases. Jena's query language, RDQL, and the Web API are both offered for the next round of standardization.

/pdf/jena-implementing-the-semantic-web-recommendations-1y9j1osjb1.pdf

Jena: implementing the semantic web recommendations

Digital Divide: Civic Engagement, Information Poverty, and the Internet Worldwide. Pippa Norris. New York: Cambridge University Press, 2002. 303 pp. $60 hbk., $20 pbk. Forecasts that the Internet heralds a world of more democracy and less poverty seem as inflated as dot.com stocks. This rosy view has electronic voting, political chat rooms, and email access re-engaging apathetic publics in politics. Digital technologies redress economic disparities, and the benefits of the Internet percolate down to transform poor societies. Equally exaggerated is the gloom of naysayers. The Internet Age has done little to narrow the gap between rich and poor countries, the information haves and havenots, cyber-skeptics contend. Indeed, digital technologies could create new inequalities and reinforce the dominance of power elites. In her new book, Digital Divide, Pippa Norris, associate director of the Joan Shorenstein Center on the Press, Politics and Public Policy at Harvard University, steps into this fusillade of cyber-hyperbole, lowers the decibel with a well-written and thoughtful examination of Internet use and access in 179 countries and dissects the claims and counter-claims. Her research and findings place her on middle ground, somewhere between current reality and optimism. The Internet era seems to be changing "politics as usual" in a number of countries, expanding and loosening information about governments and politics, allowing the entrance of new political players, and fostering international movements on the environment, women's rights, and other issues across borders. The disappointment is that digital technologies are activating the already politically active and passing up the disengaged and uninterested. A major challenge to digital democracy is the gulf between the United States, Scandinavia, and other early Internet adopters and the rest of the world. That gap is now so wide that at the turn of the century, more than three-quarters of the online community lived in the developed world. Internet use tracks the path of economic and technological development. But that situation could begin to change, Norris says. The Internet is in its technological adolescence. Costs of access are falling. And governments can make a difference if policymakers take the initiative. We have the historical patterns of other communication technologies to study. Norris examines theories of technological diffusion and points out that the American response to the Internet is more akin to the rapid spread of televisions and VCRs than the slower adoption of telephones and radios. American dominance could recede as Internet access grows worldwide. Contrary to what officials of the Bush Administration contend, Norris finds that the digital divide between rich and poor within the United States remains substantial. Europe mirrors that trend. In the long run, the Internet could become more accessible to the excluded: lower income families, minorities, and women. …

Digital Divide: Civic Engagement, Information Poverty, and the Internet Worldwide

Complexity has undesirable effects on, among others, the correctness, maintainability, and understandability of business process models. Yet, measuring complexity of business process models is a rather new area of research with only a small number of contributions. In this paper, we survey findings from neighboring disciplines on how complexity can be measured. In particular, we gather insight from software engineering, cognitive science, and graph theory, and discuss in how far analogous metrics can be defined on business process models.

/pdf/a-discourse-on-complexity-of-process-models-5ftip1g4e8.pdf

A discourse on complexity of process models

Up to now there is neither data available on how many errors can be expected in process model collections, nor is it understood why errors are introduced. In this article, we provide empirical evidence for these questions based on the SAP reference model. This model collection contains about 600 process models expressed as Event-driven Process Chains (EPCs). We translated these EPCs into YAWL models, and analyzed them using the verification tool WofYAWL. We discovered that at least 34 of these EPCs contain errors. Moreover, we used logistic regression to show that complexity of EPCs has a significant impact on error probability.

/pdf/detection-and-prediction-of-errors-in-epcs-of-the-sap-21zrtnkvxm.pdf

Detection and prediction of errors in EPCs of the SAP reference model

In this paper we present a novel scenario-driven role engineering process for RBAC roles. The scenario concept is of central significance for the presented approach. Due to the strong human factor in role engineering scenarios are a good means to drive the process. We use scenarios to derive permissions and to define tasks. Our approach considers changeability issues and enables the straightforward incorporation of changes into affected models. Finally we discuss the experiences we gained by applying the scenario-driven role engineering process in three case studies.

A scenario-driven role engineering process for functional RBAC roles

Business process models play an important role for the management, design, and improvement of process organizations and process-aware information systems. Despite the extensive application of process modeling in practice, there are hardly empirical results available on quality aspects of process models. This paper aims to advance the understanding of this matter by analyzing the connection between formal errors (such as deadlocks) and a set of metrics that capture various structural and behavioral aspects of a process model. In particular, we discuss the theoretical connection between errors and metrics, and provide a comprehensive validation based on an extensive sample of EPC process models from practice. Furthermore, we investigate the capability of the metrics to predict errors in a second independent sample of models. The high explanatory power of the metrics has considerable consequences for the design of future modeling guidelines and modeling tools.

Understanding the Occurrence of Errors in Process Models Based on Metrics

We present an approach that uses special purpose role-based access control (RBAC) constraints to base certain access control decisions on context information. In our approach a context constraint is defined as a dynamic RBAC constraint that checks the actual values of one or more contextual attributes for predefined conditions. If these conditions are satisfied, the corresponding access request can be permitted. Accordingly, a conditional permission is an RBAC permission that is constrained by one or more context constraints. We present an engineering process for context constraints that is based on goal-oriented requirements engineering techniques, and describe how we extended the design and implementation of an existing RBAC service to enable the enforcement of context constraints. With our approach we aim to preserve the advantages of RBAC and offer an additional means for the definition and enforcement of fine-grained context-dependent access control policies.

/pdf/an-integrated-approach-to-engineer-and-enforce-context-1amr8bac7x.pdf

Gustaf Neumann

Papers

A discourse on complexity of process models

Detection and prediction of errors in EPCs of the SAP reference model

A scenario-driven role engineering process for functional RBAC roles

Understanding the Occurrence of Errors in Process Models Based on Metrics

An integrated approach to engineer and enforce context constraints in RBAC environments