External representation

In this chapter, we present an attempt to put these ideas into practice that has three components. First, we use a Model of Modelling , an external representation of the mental processes that we postulate to be undergone as a person forms a model. Second, this model is exemplified by its apphcation to the design of a teaching sequence about a key topic in chemistry, the imderstanding of which requires fluency of mental movement between the three levels of representation. Lastly, this application is implemented in such a way that the processes of students thought taking place can be monitored. 

As discussed in detail elsewhere (e.g., see Cleveland, 1985 Kosslyn, 1985,1989 Liben, 1997,1999 Tufte, 1983 and Tversky, this volume), there are many forms of external representations. Among them are diagrams,... 

Mammino L. (2008). Teaching chemistry with and without external representations in professional environments with limited resources. In Gilbert J.K., Reiner M. and Nakhlekh M. (Eds.), Visualization Theory and Practice in Science Education. Dordrecht Springer, 155-185. 

Layer 2 provides the external representation of all engaged tools. Until now, there is no possibility to describe all details of the participating tools (e.g., the sequences of the commands enacted inside tools are not represented). Tools are just seen as black boxes that support the execution of specific process steps. 

A data type is necessary to allow the RDBMS to accurately convert the data from an external representation, most often text in a file, to an internal representation of the data. For example, the external representation of a numeric value is a text string containing at least one numeral, and possibly a plus or minus sign or a decimal point. A text value may contain any valid text character, usually only printable characters from the ASCII set. The internal representation of the data is dependent upon the particular RDBMS and hardware being used. It is not necessary to know the exact internal representation of the data. The important thing to consider is which data type accurately represents the data for your purposes. 

As with all data in an RDBMS, there is an external and internal representation of data. This was discussed in an earlier chapter for standard data types, such as text and numeric. For molecular structures, there is of course no SQL standard. When building a database containing molecular structures, a decision should first be made which internal representation will be used and which external representation. 

The external representation of molecular structure is a less rigorous definition. For example, there are many programs available that can convert to and from SMILES and molfiles. These can be used when a molfile (the external representation) needs to be imported as a SMILES (the internal representation) into the database. Similarly, a SMILES can be easily exported as a SMILES or converted to a molfile or other file format. It is useful to have these conversion functions as SQL extensions. 

When using a composite data type, the external representation of the value is different than the basic SQL data types. The components are represented as usual for number and text data types, but parentheses are used to associate the component values. For example, (1.74,nM) is the external representation of the cone value 1.74 nanoMolar. The following SQL produces sample output for an arbitrary compound id. 

The external representation of this data type uses parentheses. This can be awkward, so the following input and output functions are defined. 

It is always possible to use the ordinary external representation of the range data type using parentheses, but using range format and range text conforms to more common representations of data like these. It is possible to automate the range to text conversion even more, using the create cast SQL command, as follows. 

The column coord is a two-dimensional array of float values. The external representation of array data uses curly braces. For example ... 

The molfile or sdf file format is a very common way to store molecular structures. This can be considered as an external representation of a molecular structure data type. There are many other common file formats in use and only the essential features common to all of them will be considered here. The essential aspects of molecular structure contained in these files are atomic number or atomic symbol, formal atomic charge, bonded atom pairs, and bond orders. These are the minimum attributes necessary to define an unambiguous valence bond molecular structure. Other atom properties, such as atom types might also occur in these files, but these are specific to particular modeling programs and will not be discussed here. Sometimes molecular properties are also stored in these files. A way to store these properties in relational tables is discussed. 

Serious incidents are reported immediately and investigated by a team that includes appropriate external representation ... 

With respect to organizational citizenship behavior and external representation behavior, role conflict and associated job stress may become more salient in embedded lead users. E.g. internal and external expectations may be conflicting in external representation behavior. Representing and praising the firm towards peer users, when embedded lead users know, that competitor product hold more use value, will lead to role conflict For these behaviors, growing lead userness may be associated with growing role conflict Thus, the effect of lead userness on these behaviors may be folly mediated and evened out by role conflict Further research is needed on these two countervailing forces and their impact on embedded lead user s behavior. 

Embedded lead users are passionate about the product domain, but not necessarily about the employing firm s products or the firm itself. They are highly motivated to engage in behaviors connected to users and products (potentially in rather specific niches] if and as they and their peers stand to benefit Their organizational commitment and loyalty may be less pronounced, depending on various factors. The data offers preliminary support of this being the case in my research context External representation and organizational citizenship behavior of the firm does not increase with embedded lead userness. 

---