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资源说明：1990's Code dump; shell tools to convert Oracle views into class-like C structure scaffolding
NOpGen and GROG
History
Sun 6-13-1993, Sun 8-29-1993
When I began this database course, I had no idea it would stretch on this long,
let alone that I would have so little time to put towards it. I began in the
fall of 92, and was waylaid by a change in jobs as well as the birth of my
son Craig. I have also been spending more than my share of time on work
related efforts, for which I hope to be compensated. Nevertheless, it has
had a severe impact on my ability to live up to my school related, and self
imposed, obligations.
For this last point I am regretful; the completion of this degree program
means a lot to me personally both in terms of my own accomplishments as well
as the hoped for effects it will have on my carreer. At the same time, being
a member of the R.Buckminster Fuller Institute, I have an eye for keeping
things in perspective. It may take longer to understand situations and
approaches as a comprehensive design scientist, but when you're done you
really have an excellent grasp of the whole picture.
During the fall school year of 92-93, I implimented a lexer and parser for
a text processing language I termed the Northside Operations Generator,
or NOpGen. NOpGen was implimented in about 1000 lines of commented AWK
code (GNU gawk). It is a language for defining and instantiating
templates of text, and really stretched the capabilities of AWK to the
maximum. Rather than discuss the language again here, I will simply
point out a few unique features. First, it consists of only a few
language constructs and keywords: COUPLING, BLOCK, and PASTE, which
(with the NOpGen semantics) it is possible to describe and generate
fully customizable source code, text documents, etc. Second, unlike
most macro and template languages, NOpGen explicitly recognizes the
dependencies which exist between source code and entities external and
internal to the system, such as database schemas, file systems, human
programmers, hardware configuration settings, & etc.
The text processing flow of the generator was modelled after the
sequence of events during a typical database application coding session
between a programmer and a text editor - hence the use of the keyword
PASTE. In my own experience I quickly recognized that, especially with
data strong applications, certain patterns emerged which repeated
themselves over and over in the source code - hence the use of the
keyword BLOCK (a block or template of text). Lastly, as I had recently
been working in an X11 windowed environment, it struck me that one of the
most frequent situations which arose was of having an editing session open
in one window, while concurrently opening, reviewing, cutting from, and
closing windows into other areas of the system - especially to a database
or a command line shell.
What I and thousands of other programmers do - routinely,
repetetively, and often with drudgery - is to act as a kind of plumber
to reroute information flows from one portion of the system to another.
The difference between us and plumbers is that they know how to accomplish
the task once with pipes and fittings, while we seem to be content at doing
it over and over again using the equivalent of buckets. This is where the
use of the keyword COUPLING came from, as an analogue to a fitting between
pipes. All he thinking for this went on over the five years prior to the
first implimentation of NOpGen. Quite a few years into this time, unbeknownst
to myself, Microsoft Corp. released an application programming interface
relying on a similar concept called Direct Data Embedding, or DDE, which
they have lately extended to Object Embedding and Linking. IBM has also
implimented forms of this technology in its OS/2 operating system. But I
have to this date yet to see anyone beside me apply the ideas to source
code creation and maintenance. In a way it is quite sad, as it doesn't
say much for the state of the practice, but it is nice to know that "one
lone, average human being" can be on the bleeding edge of the technology.
GROG, the name, started long ago in the mind of a child. I thought it
would be an interesting name to use for a new software development tool,
method, or technology. It wasn't until the recent course in database
programming that I had a suitable candidate for the name. So GROG doesn't
really mean anything, but if you wanted it to, it could mean
'Generalized Object and Relational Generator' or something like that.
This is my preferred meaning, and it accurately reflects the intentions
of the course project, which is to apply some fundamental object oriented
techniques to an existing relational database sofware system.
The GROG implimentation was originally started as a package built
through NOpGen. NOpGen blocks were written which provided textual templates
for the creation of C structs, macros, functions, and anciliary state
variables. Default shell scripts were written to mimic the way a database
engine might respond to queries, to provide working stubs for NOpGen couplings.
A relational table structure was worked out to provide a queriable repository
of class and method definitions, as well as declarations of
instance-connections, whole-part structures, and generalization-specialization
structures. The combination of couplings, blocks, and paste directives,
when run through NOpGen (with enough information for a meaningful coupling
context available) was intended to instantiate a source code library
of class and object definitions, with C macros used to provide a syntactically
sweet way of referencing and manipulating the objects.
One major problem I ran into, which stalled me at a critical time (just
before my wife went into labor), was that C macros are not available to
externally compiled modules. Furthermore, the macro language of the CPP
preprocessor is very, very simple, and I could not produce both a definition
of a locally named object as well as a direct reference by name to that
object, as you might in ordinary C or C++ code. What I wanted was:
type_customer myCustomer;
type_customer *customerArray[20];
customerArray[0] = &myCustomer;
myCustomer.print();
customerArray[0]->print();
This seems like it would be easy at first glance, since the syntax is
already supported by the C language for the 'struct' construct. Why not
just use function pointers for the print() method? It is not so simple,
however, since if you use a 'typedef struct' for type_customer, the
print() element of the struct is uninitialized and therefore cannot be
referenced without programmatically tragic consequences ('segmentation fault
- core dumped' is the most usual). A more minor inconvienience is that
the '.' (dot) operator cannot be used for the print() member, since it
would have to be declared as a 'pointer-to-function' rather than a 'function'.
An even greater complication would arrize from attempting to use the C
macro preprocessor to assist in the declaration and initialization of
object types, since it is not possible to control the placement of such
macros or debug errors caused by incorrect usage of them. Furthermore,
the use of a seperate, special purpose preprocessor would require that
all application code referencing the objects be precompiled by the GROG
system. Still another problem arises when one wants object declarations
to automatically initialize the object to a known consistent state - to
hold to invariants. Most ESQL/C implimentations throw up code which makes
perfectly legal ANSI C constructs such as
int i=0;
Product **catalogue = Product.Locate( "Hammer", "Saw", "Knife" );
int j=1;
because most ESQL/C precompilers and their base C compilers still go by
broken/archaic C standards, which do not allow variable declarations
intermixed with function calls. This leaves a very big hole in the
validity of the resulting program, as there is no mechanism for ensuring
that the object constraints are always met. A known limitation. The
programmer must instead do the error prone
int i=0;
Product **catalogue;
int j=1;
catalogue[0]->Print(); /* ERROR ! ! ! Segmentation Violation ! ! ! */
catalogue = Product.Locate( "Tray", "Brads", "Screws" );
Again, any application code referencing the objects must have
access to the most current versions of the implimentation, and must have
the access macro's defined prior to the preprocessing of it's compilation
unit. Strange compiler errors - or worse, no errors and undefined behavior
- could result. To prevent syntactic and logical errors from being
inadvertently inserted, the precompiler would require knowledge of C syntax,
which I am not sure is within the scope of this project. I may leave this
last item as a 'known limitation', and do it anyway.
I thought of placing the source code referencing the objects directly
into the database tables, so that it can be guaranteed to reference only
the correct macros and structure definitions. After having worked with
an RDBMS application development environment which does this (Oracle), I
no longer think this is a good idea. It is too monolithic and centralized
an approach, and lacks access to the bevy of traditional library, archiving,
and change control tools available to flat-file managed source code. Source
code is also of arbitrary length and has no useful relational structure,
which makes it difficult to manage using the RDBMS provided mechanisms.
Let me recap the ideas I've had so far. First, I have thougth of placing
the GROG meta-data into a set of GROG system tables. This meta-data
describes the classes, methods, and structures known about by the system.
Second, the classes, methods, and structures would be 'instantiated' through
the use of predesigned code templates and a GROG class definition export
utility. Third, the protocol for accessing the objects is to be virtually
identical to that of C++ object references and declarations, vis a vis
Customer myCustomer;
Customer *customerArray[20];
customerArray[0] = &myCustomer;
myCustomer.Locate("Bob Cratchet");
customerArray[0]->print();
with a known limitation that object initialization must be performed as a
manual coding task, rather than automatically. Fourth, in a C
environment, '.h' header files would be used to contain the class
declarations and macro definitions, while '.c' and/or '.pc' source files
would contain the method definitions, which would be placed into an 'ar'
object code library. Source files which need to access
the classes would "#include" the header file and specify the necessary
'ar' library on the compiler command line. Fifth, a small number of useful
method definitions would be included along with the user defined methods
by default, to ease in code construction. Some potential defaults would
include constructors, destructors, and locators. Sixth, only the method
names would be stored with the GROG system meta-data. The method definitions
themselves, including templates for the defaults, would be stored in
operating system flat files, with additional management provided by
configuration management tools like RCS, SCCS, Make, & etc.
A seventh item was to be included here, which featured a step
in which all code which references objects must be run through a seperate
preprocessor. Declarations such as the ones above mentioned
could then be initialized automatically. The idea was discarded due to
the large number of syntax holes it would introduce.
Item seven was likely to involve the insertion of CPP '#define' macros
rather than statements of C code. It was to turn this:
Customer myCustomer;
Customer *customerArray[20];
customerArray[0] = &myCustomer;
myCustomer.Locate("Bob Cratchet");
customerArray[0]->print();
into this:
Customer myCustomer;
#define mycustomer.Locate(x) grgCustomer->Locate( &mycustomer, (x) )
Customer *customerArray[20];
customerArray[0] = &myCustomer;
myCustomer.Locate("Bob Cratchet");
customerArray[0]->print();
Unfortunately, most macro processors on Unix systems today do not
support punctuation characters (eg. '.') in the macro names. Furthermore,
the macro does not fully support the underlying data structuring
capabilities in 'C'; the array operator '[]' is an anomaly here - the last
call to member function Customer.print() through customerArray[0]
will not compile.
Rather than writing a new compiler to handle such deviations, I decided
to eliminate the need. The GROG object specification protocol instead
allocates method pointer members as part of the class definition
structure. As an added feature, GROG also predefines methods for
object construction, destruction, persistent storage insertion and deletion,
object and member validation, and object and member formatted output.
There are two features to note in this approach. First, since every variable
of a given object class gets its own local copy of the method pointers, any
'C' data structure containing that variable can access its methods. The
syntax is limited to the obtuse pointer->member operation, but it is quite
workable. Second, pointers to the predefined methods can cause the
size of the object class definition, and of resulting variables, to balloon.
This is because validate and print methods are predefined for not only
the object class, but all of its data members as well. With many large
tables, the resultant application is likely to be gigantic.
Technical details of the approach taken with GROG, such as a template
of its output protocol, can be found in the GROG Technical Reference Manual.
Known bugs and limitations which have not or will not be fixed are detailed
in the Release Notice. Information on what tasks can be performed with
GROG, and how to perform them, can be found in the User Guide.
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