QL-RTDB: QUERY LANGUAGE FOR REAL-TIME DATABASES

Cic

ılia R. M. Leite, Y

askara Y. M. P. Fernandes and Angelo Perkusich

Electrical Engineering Department

Federal University of Campina Grande, Campina Grande - PB

Pedro F. R. Neto

Informatic Department

State University of Rio Grande do Norte, Mossor

o - RN

Maria L. B. Perkusich

Informatics and Statistics Department

Catholic University of Pernambuco, Recife, PE

Keywords:

Real-Time Systems, Real-Time Databases, Query Language.

Abstract:

In the last years, many research directed for concurrency control mechanism, scheduling policy and query

language in real-time database are being done. This paper presents an extensions of standard query language

(SQL), called SQL-99. SQL-99 includes oriented-object functionalities. The query language for real-time

database (QL-RTDB) to provide support the real-time requirements imposed the both data and transactions. A

prototype implementation of the QL-RTDB is also shown.

1 INTRODUCTION

Real-time databases (RTDB) are typically used to

manage applications with critical data. Among these

application is programmed stock trading, medical pa-

tient monitoring, automated manufacturing, and mili-

tary command and control (PRICHARD, 1995). The

RTDB project has to take in consideration character-

istics of traditional database system (DBMS), and of

real-time system. The RTDB must keeping data in-

tegrity, and to guarantee timing constraints to both

transactions and data (STANKOVIC et al., 1999).

Consequently, the data must not only be logically

consistent, but temporally consistent as well for these

applications. This is due to the fact that data used

by critical time applications must closely reﬂect the

current state of the environment application.

However, although some researches directed to-

ward real-time database, new approach must be pro-

viding by these, related the concurrency control,

scheduling policy and query language (TESANOVIC

et al., 2002; FERNANDES et al., 2004; LIND-

STROM, 2002; PRICHARD, 1995).

In the query language conception, the data deﬁni-

tion, data manipulation, and transaction control must

to be provided. Data deﬁnition is made through of the

data deﬁnition language (DDL). Data manipulation is

realized through of the data manipulation language

(DML). The transaction control includes commands

for speciﬁcation of transactions (ELMASRI and NA-

VATHE, 2004).

However, the available query language not supports

complex applications with timing constraints. In this

way, the deﬁnition of a query language becomes im-

portant to support such restrictions (SUDARSHAN

et al., 2001). The objective of this work is deﬁne a

query language to support requirements of timing to

both data and transaction, called QL-RTDB. This will

consist in extending SQL-99 (O´NEIL and O’NEIL,

2000; STEPHENS and PLEW, 2003; STEEB, 2004).

This work is organized as follow: in Section 2, we

present related works. In Section 3, we describe the

basic characteristics of RTDB. In Section 4, we show

the SQL-99. In Section 6, we deﬁne an extension of

the SQL-99. Finally, in Section 7, summarizes the

main ideas of the paper and describes futures work.

2 RELATED RESEARCH

In the context of RTDB, a query language, called real-

time SQL (RTSQL), was developed in (PRICHARD,

1995) as an extension of standard SQL-92. SQL-92

is a language that allows us to query and manipu-

420

R. M. Leite C., Y. M. P. Fernandes Y., Perkusich A., F. R. Neto P. and L. B. Perkusich M. (2005).

QL-RTDB: QUERY LANGUAGE FOR REAL-TIME DATABASES.

In Proceedings of the Seventh International Conference on Enterprise Information Systems, pages 420-423

DOI: 10.5220/0002524404200423

 SciTePress

late data on relational database system (O´NEIL and

O’NEIL, 2000). RTSQL is deﬁned to support real-

time queries, including extensions that specify the

temporal consistency of the data and transactions. A

prototype developed in C, was implemented to vali-

date and to test the correctness of them.

In 1999, a new standard, called SQL-99, was

published by American National Standards Institute

(ANSI) and International Organization Standardiza-

tion (ISO) for the object-relational model. This stan-

dard extends the SQL-92 to include oriented-object

functionalities (O´NEIL and O’NEIL, 2000). How-

ever, the SQL-99 does not consider the deﬁnition and

manipulation of data with timing constraints. In this

way becomes necessary the development of exten-

sions for the SQL-99 in order to attend the timing

constraints.

3 REAL-TIME DATABASE

A real-time database system has three distinguish-

ing features: the requirement of temporally consistent

data, the requirement of timing constraints on execu-

tion, and the requirement that certain execution ex-

hibit predictable timing behavior. These features are

useful to time critical applications that need to collect,

modify, and retrieve shared data. Support for these

features will add new requirements to the DDL and

DML of the database query language (PRICHARD,

1995).

Like a conventional database management systems,

an RTDB must process transactions and guarantee

that the database consistency is not violated, besides

to keep time constraints or deadlines for transac-

tions as well as the timing validity of the data (BE-

STRAVOS et al., 1997). The performance goal for

these systems is usually expressed in terms of the de-

sired average response times, rather than constraints

associated to individual transactions. Thus, when

the system makes scheduling decisions, individual

real-time constraints are ignored (STANKOVIC et al.,

1999).

The temporal consistency can be measured through

of the absolute consistency and of the relative con-

sistency of the data. The absolute consistency is the

measure between the state of the environment and as

it is reﬂected in the database. The relative consistency

is the measure between the data that are used in the

computation of other data (Bestravos et al., 1997).

The real-time data can be deﬁned for tuple

(nr, vrr, avir, tsr, impr), where: nr is the data item

processed; vrr is the value that is updated for the item

in server; vrr is a exclusive ﬁeld of server and its

value is obtained of the environment; avir is the ab-

solute validity of data, i.e., the time that the data is

considered valid after transaction begins; tsr is the

timestamp of data; impr is the exported collected im-

precision (Ribeiro Neto et al., 2004).

In this work, we will consider that transaction are

deﬁned by the quadruple (tl

, tc

, pr

, pe

), where: tl

is the transaction release time, that is, the moment in

which all the necessary resources to the execution of

the transaction τ

are available. Starting from this in-

stant of time the transaction is ready to be executed;

deﬁnes the transaction computation time, that is,

the processing time necessary to execute it; pr

de-

ﬁnes the maximum transaction execution period, and;

deﬁnes the periodicity of the transaction.

4 SQL-99

Committee ANSI/ISO SQL-99 introduced a standard

query language that supports the object-relational

model. The SQL-99 to provide a series of new capa-

bilities: user types deﬁned; collection types, such as,

vectors or table nesting; and methods and user deﬁned

functions (O´NEIL and O’NEIL, 2000; STEPHENS

and PLEW, 2003).

User Deﬁned Types (UDT) - It is a nominated

group of attributes of different types of data (objects)

that can be used to deﬁne tuples of a table or the type

of some attribute of a table.

Collection Types - A column value (on a single

row) to contain a set (or some other type collection,

such as an array) of row-like values. In some systems

a single column value can itself hold a table, a feature

know as table nesting.

Methods and User Deﬁned Functions (UDF) - In

object-oriented languages such as Java, any private

data in a object can be accessed only via object meth-

ods, such methods are functions that can be invoked

to operate (ECKEL, 2002) on one particular object.

Normally, the set of methods for an object will deal

with all properties of the object that can be treated in

isolation (O´NEIL and O’NEIL, 2000).

Therefore, the speciﬁcation SQL-99 extends the

SQL-92 standard including object-oriented function-

alities (O´NEIL and O’NEIL, 2000). Some commer-

cial DBMS as: DB2, PostgreSQL, Oracle9i, among

others, already implement SQL-99.

5 SQL-99 EXTENSION

Real-time programming languages must provide

mechanism to deﬁned timing constrains, used to ex-

press the start times, periodicity, release time and

deadlines (or completion times) of transactions. To

satisfy such constraints, the query language also must

to incorporate these properties.

QL-RTDB: Query Language for Real-Time Databases

421

Considering the exposed above, in this paper we

will extend the syntax of the DDL of the SQL-99 to

consider beyond the deﬁnitions of the logical con-

straints, the deﬁnitions of timing constraints of the

data, such as: timestamp, and absolute validity of

data. The syntax of the DML and the transaction

control will be extended in order to consider timing

clauses, such as: start time, release time, transaction

periodic, computational time, deadline, among others.

6 QL-RTDB

The QL-RTDB was implemented in the java pro-

gramming language. Java is multiplatform, allow-

ing that programs can be executed in machines with

different operational systems, guaranteeing the porta-

bility of any application implemented in this lan-

guage (ECKEL, 2002). Speciﬁcally, we utilized the

real-time speciﬁcation for Java (RTSJ), so that this

available extensions for real-time applications (RTS,

2003).

After Transaction

Figure 1: Query Transaction

For the QL-RTDB implementation, the DB2 was

utilized as the data repository. For this, was necessary

to establish the connection of the QL-RTDB applica-

tion with the database through of driver JDBC (Java

DataBase Connectivity). Then, we load driver for the

database in the Java Virtual Machine (JVM) of the

application. The driver is registers to DriverManager

and is available for the application. We use the classe

DriverManager to open a connection with the data-

base. The interface Connection it assigns an object,

in the case con, to receive the connection established.

We present the QL-RTDB language through of Fig-

ure 1. This shows the transaction T1 that is a query

transaction. The time parameters and logical para-

meters are passed through of clauses for the RTDB,

where the information will be stored in the database,

for latter query, updates and reports.

The query transaction T1 verify the absolute con-

sistency of the data through of expression ((t−tsr) ≤

avir), where t is the current time; tsr is the data

timestamp; avir is the data absolute validity. The

query result, illustrate in the table of Figure 1, show

whole data temporality consistent. The table ﬁeld was

deﬁning in the Section 3.

7 CONCLUSION

In this article we made a state of art survey from about

query language, where each work has its speciﬁcation

and its contribution. Thus, we search extract the con-

tributions of each work and to adapt to our context.

We deﬁne a query language for real-time database,

called QL-RTDB, that providing support the real-time

requirements imposed the both data and transactions.

A prototype implementation of the QL-RTDB is also

shown. We choose the programming language java

for real-time, due to this permitting extension, and

oriented-object. As future work, we will add func-

tionalities with timing parameters. These function-

alities are speciﬁed through of the DDL, DML and

transaction control.

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