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Purpose
When modernizing an application, there is frequently a need to identify and extract portions of the application that contain key business logic so that they can be incorporated into the new version of the application. The Harvesting Editor is intended to facilitate this process by using a rules-based approach to separate what is probably important business logic from the artifacts of the architecture which surrounds it so that a programmer can more easily identify useful code fragments and capture them in a way that they can be re-used. We will use the term “wheat” to identify code which is a good candidate for harvesting and “chaff” for code which we are unlikely to want to harvest.

Context
When companies have an aging legacy application, their options are to continue to try to work with the application as it is, to write a fresh new application, or to attempt to transform the existing application (See http://www.psdn.com/library/entry.jspa?externalID=961&categoryID=58 for a discussion.). Some form of application transformation tends to be the option most likely to produce good results at reduced risk and with controlled cost.

There are several different approaches to application transformation including the formal Application Transformation Approach (ATA) advocated by Progress® (see http://www.progress.com/progress_software/products/services/docs/at_ment... ). Another approach which has recently been discussed in various forums, but without a formal name, is installing an ESB/SOA environment and then progressively converting targeted sections of code into services, a sort of “Getting on the Bus, gradually” approach. Most of these approaches involve a combination of creating new code and harvesting key business logic from existing code. (see http://www.progress.com/progress/ptw/2005/emea/docs/ptw_061.ppt for a discussion in the context of ATA). This current project is aimed at helping the process of harvesting and reusing code from existing applications.

A PDF of the full article is available below, which include illustrations not available here

Background
One of the confounding facts in any attempt at architectural modernization is that a great deal of the code in any application is predictable based on the application architecture and the context. Since both the programmer and person paying the programmer are often impressed with the amount of work required to create the code in its current form, this probably deserves some explanation.

Consider the case of the simple file maintenance functions that provide the foundation for any application. Unless there has already been some architectural modernization in the life of the product, chances are that all of these functions within a given application have a great deal of similarity.

Part of these functions is predictable based on other key information, i.e., it derives from the data dictionary and the relationships between tables. Another significant portion of these functions is simply “the way we write file maintenance programs in the current architecture”. It is only what is left when these two aspects are removed that constitutes unique business logic, e.g. validation rules not contained in the dictionary. It is only this portion that is of interest in harvesting.

Thus, if one is migrating to a new architecture and thinks of the same file maintenance functions there, they will also be largely predictable from the data dictionary and those small bits of business logic. In both contexts, the bulk of any program is “chaff” and the wheat is limited to the pieces related to the data dictionary and the small bits of business logic.

Of course, applications don’t consist entirely of file maintenance functions, but similar statements apply to inquiry functions and simple list reports. The same principles even apply to many transaction entry functions since those often consist of what amounts to a file maintenance operation coupled with some piece of business logic that creates the impact of the transaction. This means that there is likely to be more business logic than in a simple file maintenance function, but it doesn’t necessarily imply that the basic portion that deals with creation, deletion, and editing of records is any different than the file maintenance case.

Harvesting, then, is the process of identifying these pieces of business logic in the midst of all of the other existing code. In some cases, the target can be reasonably apparent because a particular function represents a key transaction in the system, for example. But, in the case of the smaller pieces of business logic which are embedded in large amounts of largely predictable code, it can take considerable effort to identify the desired fragments so that they can be preserved and re-used.

Concept
In the technology of harvesting, there is a continuum between a totally manual review of code at the low end to a hoped for future tool in which all code in an application will be automatically converted to UML, ready for generating a new application. The current project proposes to create a tool which lies between these extremes by using a rule-based structure to assist in determining what is wheat and what is chaff within any given body of code so that the analyst can review the probable wheat and extract it for re-use as appropriate.

It is expected that this goal will be approached in several stages, starting with fairly simple rules which depend only on the code being examined, but later extending to interactions with previously extracted models. In the initial stages, the concept is that we will “gray out” and possibly collapse sections of code which have been evaluated as chaff in order to enable the analyst to review the remaining code more easily and to evaluate it. If it is evaluated as chaff, then the analyst should be able to mark it and collapse it further in order to focus on what remains. In later versions, more sophisticated rules will interact with previously harvested code to determine, for example, whether a particular fragment has already been harvested in another context. Some code fragments, e.g., validation rules, are likely to occur repeatedly in legacy code.

In initial versions, we expect that the actual harvesting will be simply cutting and pasting from the editor into whatever vehicle is going to be used to store prospective logic fragments. In later versions, we would hope to have a more automated process which will directly transfer selected code to a new form, either as a separate code unit or as a component of a model.

While it would be desirable to support all forms of harvesting including cutting and pasting to new .i and .p files, there is a special attraction for supporting harvesting to UML because, in addition to the potential of UML modeling itself, there would be the possibility of predictable relationships between harvested code and components of the UML model. For example, a field validation would normally be stored as a constraint on an object property, so a field validation in the code could be checked against the object property to determine whether this constraint had already been harvested. To do the same with .i and .p files would require a very artificial naming convention.

Initial Rule Set and Operations
In the initial implementation, the goal will be to classify any one block of code as wheat, chaff, or unknown, where “wheat” is material considered a good candidate for harvesting, “chaff” is material considered to be unlikely to be worth harvesting, and unknown is anything that doesn’t fall into either category. Chaff sections will be indicated by a 15% grey background; wheat sections by blue text; and unknown sections by black text. Sections will be boxed or delimited in some way so that one can easily select the whole section. Ctrl-Plus will “promote” a section from chaff to unknown and unknown to wheat; ctrl-Minus will “demote” a section from wheat to unknown and unknown to chaff. Ctrl-[ will collapse a marked section to a single indicator line; ctrl-] will undo the collapse to visible text. Ctrl-C can be used to copy an entire section to the clipboard for use in pasting into the desired harvesting repository.

Initial rules to identify “chaff” will be:

  1. All DEFINE statements. While the variables defined may be needed for harvested wheat code, that code will typically be packaged differently than it appears in the source program and is likely to be refactored. Thus, one generally won’t want to capture the variable definitions with the code because the definitions in the harvested code are likely to change in form. Also variable definitions are often widely separated from their use, making harvesting them both as a unit difficult.
  2. All lines consisting only of whitespace. Trailing whitespace will be included in a preceding chaff section; preceding whitespace not already included in a chaff section below will be added to a chaff section which trails it. Alternatively, an option might be provided to simply eliminate any whitespace.
  3. All include references, although one can drill down into the include and harvest from it as well. Include references themselves are marked as chaff because it is extremely unlikely that they will be harvested as such.
  4. Simple assignments including:
    1. Simple assignment of a value from a database table to a local or shared variable.
    2. Assignment of literals to a local or shared variable.
  5. All UI updates and displays.
  6. Access to “system” tables, a user provided list.

Comments (see below).

Initial rules to identify “wheat” will be:

  1. FORM, DEFINE FRAME, and implicit FORM statements that define UI layout. These are included based on the assumption that one will be trying to capture the general screen layout, e.g., in a fashion similar to Pro/Dox, even though the details of the UI and the technology of its display will be significantly different in the rearchitected code.
  2. VALIDATE statements for database fields (might check dictionary and/or a good early candidate for checking previously harvested code per some convention).
  3. Flow of control logic. A flow of control block whose contents are entirely UI statements or other chaff will be considered chaff as well.
  4. Database access other than to “system” tables.

Note that the simple assignments rule does not include any assignment in which there is computation, since that might be an indicator of a business rule. Some form of the simple assignment might be required to supplement a harvested piece of logic in order to provide appropriate initial values, but these assignments are moderately likely to be of a different form than in the source code. It is also common for them to be physically removed from the place where the value is used. Note also that while the values associated with such variables may well be important in determining control flow, most such control flow will not be harvested in the form it is in. E.g., a file maintenance program might have sections for creating, modifying, or deleting a record depending on whether a record already exists with the specified key and/or some user input. While the code in each section related to what one does to create a record, modify a record, or delete a record may be captured in three code fragments, the control flow leading to those blocks is a part of the local architecture of the old program and will be implemented differently in a new architecture.

While possibly not in the initial implementation, it would be desirable to be able to identify blocks of code such as the following as chaff:

do for uom:
find uom of item no-lock.
display uom.description[1].
uom--code = item.uom.
end.

Here there is a strongly scoped block, i.e., we know that there are no references to the UoM buffer outside this block that are not inside their own strongly scoped blocks, and within that block there is a no-lock find, a display, and an assignment to a local variable, i.e., it should be a block of chaff.

Also, specific to the code in the samples attached, all blocks referencing init-val and condition should be chaff, but I’m not immediately sure how to make that into a rule. This highlights the need for base rules that are likely to be used with any code and site-specific rules that are added based on the particular body of code currently being harvested.

It could be desirable to eliminate all blank lines, but this would limit any tools for linking back to the original. Instead of attaching them to adjacent chaff blocks as is suggested above, an alternative would be marking them as chaff in their own right and default to displaying these as compressed.

It would probably be useful to “pretty print” to standard indentation prior to marking up the text so that the indentation was an accurate rendering of block structure.

Wheat and chaff rules should have a “weight” and a run-time option should be provided to only mark up wheat or chaff that exceeded a certain weight value. Separate values should be provided for wheat and chaff. E.g., one might assign the comments rule for chaff to -1 and then a cutoff value of 0 would mark comments as chaff and a cutoff of -1 would not. It should also be easy to simply turn a particular rule off when desired. Each chaff rule might also be associated with a flag as to whether initial display should be compressed.

A button or keystroke should be provided to bring in any individual include in the fashion of the COMPILE LIST option. A run-time preference could be provided to default to this behavior or to not bringing in the include.

An alternate treatment of comments would be to mark them as wheat or chaff according to the nature of the node to which they are associated, typically the line of code following for comments that occupy one or more lines.

Implementation
The harvesting editor will be created as an Eclipse plug-in for use in the context of the OpenEdge® Architect or independently. The mechanism for interface to a UML tool is a matter needing further study.

Consideration should be given to implementing the rules as written in an ABL subset or something that looks a great deal like ABL and then compiling these into Java for execution. This would make it considerably easier for a non-Java programmer to extend the editor for his or her own needs.

Later Developments
The long term goal is to advance this technology to the extent that we can achieve automated extractions without the need for operator intervention. When development has advanced sufficiently to begin doing automated extractions, we should probably branch the code development so that there continues to be a harvesting editor available for those who will not use our development technology.

Consideration should be given to enabling rules that will mark unused variables as chaff and which will identify any dead code.

To see sample images, download the PDF.

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HarvestingEditor.pdf135.48 KB