Note that there is a great temptation to add concrete member functions and data to pure abstract base classes. This must be resisted, in general it is a sign that the interface is not well factored. Data and concrete member functions tend to imply a particular implementation and as such can inherit from the interface but should not be that interface. Instead if there is some commonality between concrete classes, creation of abstract class which inherits its interface from the pure abstract class and defines the common data and member functions of the concrete classes works well. Some care should be taken to decide whether inheritance or aggregation should be used. Too many layers of inheritance can make the maintenance and usage of a class difficult. Generally, the maximum accepted layers of inheritance is about 3, above that and refactoring of the classes is generally called for. A general test is the "is a" vs "has a", as in a Square is a Rectangle, but a Square has a set of sides.
Eight : This is too long and detailed to be in an abstract; it sounds as though it was pulled from the methods and materials section of the paper. The amounts of enzyme do not need to be stated, nor do the pH levels. The number of samples tested do not need to be included either; it is just extraneous information that is not crucial to understanding the experiment as a whole. The information contained in this sentence can be pulled out and rearranged to say that some samples had a constant pH and varying enzyme concentrations and other samples had constant enzyme concentrations and varying pH levels. With the controls and the variables stated you can move on to your results. ( return to Sample 1 )
The categories of count and non-count nouns can be confusing, however, and we suggest further review, especially for writers for whom English is a second language. The second section we offer is called Count and Non-Count , a basic review of those concepts and their uses in sentences, with many examples. Third, we offer WORKING WITH NOUNS , a more extensive (and somewhat more advanced) review of the count and non-count distinction, along with exercises. Finally, just when you thought you couldn't stand such riches, we suggest you review the uses of Articles, Determiners, and Quantifiers with count and non-count nouns.