El BLOG de FLamelas

Estimados,

a continuación incluyo un documento en inglés que les describe una breve historia sobre el SQL así como la situación actual en la que se encuentra este importante lenguaje de las bases de datos. Espero que el mismo sea de su utilidad.

"SQL is both deep and wide. Deep in the sense that it is implemented at many levels of database communication, from a simple Access form list box right up to high-volume communications between mainframes. SQL is widely implemented in that almost every DBMS supports SQL statements for communication. The reason for this level of acceptance is partially explained by the amount of effort that went into the theory and development of the standards.

Early History

The father of relational databases, and thus SQL, is Dr. E.F. "Ted" Codd who worked for IBM. After Codd described a relational model for databases in 1970, IBM spent a lot of time and money researching how to implement his ideas. IBM came to market with a product named System/R in 1978.

But other companies had formed and created relational database products before IBM was ready to release System/R. The first to market was Relational Software's product named Oracle and the second was Relational Technology's Ingres. IBM then released improved products in 1982 named SQL/DS and DB2. Oracle (now from Oracle Inc.) and DB2 are still available today in nth generation forms while the Ingres technology was bought by Computer Associates.

Standards

As we said at the beginning, SQL is a standard, open language without corporate ownership. The commercial acceptance of SQL was precipitated by the formation of SQL Standards committees by the American National Standards Institute and the International Standards Organization in 1986 and 1987. Two years later they published a specification known as SQL-89. An improvement and expansion (to some 600 pages) to the standard gave the world SQL-92. We now have the third generation standard, SQL 99. The existence of standards is important for the general portability of SQL statements.

Current State

So the ANSI-SQL group has published three standards over the years:

• SQL89 (SQL1)
• SQL92 (SQL2)
• SQL99 (SQL3)

The vast majority of the language has not changed through these updates. We can all profit from the fact that almost all of the code we wrote to SQL standards of 1989 is still perfectly usable. Or in other words, as a new student of SQL there is over ten years of SQL code out there that needs your expertise to maintain and expand.

Most DBMS are designed to meet the SQL92 standard. Since many of the advanced features of SQL92 have yet to be implemented by DBMS vendors, there has been little pressure for a new version of the standard.

Nevertheless a SQL99 standard was developed to address advanced issues in SQL. All of the core functions of SQL, such as adding, reading and modifying data, are the same. As of early 2001, no vendor has implemented the SQL99 standard.

There are three areas where there is current development in SQL standards.

First entails improving Internet access to data, particularly to meet the needs of the emerging XML standards.

Second is integration with Java, either through Sun's Java Database Connectivity (JDBC) or through internal implementations.

Last, the groups that establish SQL standards are considering how to integrate object- based programming models.

Flavors of SQL

The computer industry (like most industries) both benefits and suffers from standards. We said that SQL is an open standard, not owned by a company, and the standard comes from ANSI. Therefore the SQL standard from ANSI is considered the "pure" SQL and called ANSI-SQL.

Two problems emerge to sully this pureness. First is that every DBMS vendor wants to differentiate their DBMS products. So if you look at the feature set of each DBMS product you see that not only does the product support ANSI-SQL but it also offers extra features, enhancements or extensions that are available only from individual vendors. For example, most vendors offer a field type which auto- increments even though this is not described in the SQL standards. These additions to ANSI-SQL are generally proprietary and will not work if you try to use them on competitor's SQL products. At the level we discuss in this book there are only very minor differences between the vendors that we will note throughout the book.

Many of these features are powerful and robust, but since they vary from vendor to vendor, programmers should use them with caution. It is always safest to stick with pure SQL whenever possible; if you stray it should be with full knowledge that you are losing the portability of your statements (and perhaps even your data).

Such enhancements are not all bad because these extensions are very useful. For example, ANSI-SQL does not contain an automatic way to assign a serial number to each new record but most DBMS sold today have added this feature. Since serial numbering is so common programmers are happy to have the enhancement. However, the method of implementation is not uniform, so code written to get the serial number from data in one DBMS may not work when used with another vendor's DBMS."

# posted by Franklin Lamelas @ 6:21 p. m.